My experiences with Belgians have been varying; The differences in temperament between lines can be remarkable.
My own Belgians tend to be very work oriented dogs who are very active outside but can turn off and relax inside. I don't like bounce off the wall dogs. I've had instructors not believe me when I tell them that my dogs are very easy dogs at home; They are absolute couch potatoes. When you work them, it's a different story; They are "up," they are ready to go! I can't sya I've known any lazy Belgians who didn't want to work at all, but I've known plenty who couldn't find that offswitch. I've seen this mostly in tervs. Dogs that can't relax, that pace in the house, that immediatly run for the door and hit it hard as soon as you get up from the couch, etc.
Though most recommend socialising Belgians a great deal, I do absolutely nothing with the puppies I keep, and they still turn out to be incredibly well rounded outgoing dogs with no environmental sensitivities (in fact the best temp I've had is in my current 6 month old pup who has probably only left my property 7 or 8 times in her life and still has never met a stranger or situation she didn't like). Of course for extra insurance, people should take puppies out lots. I like knowing that I can have an undersocialised dog with no issues. I've never bred a shy or noise sensitive dog -- but I've owned them, and I've met ALOT of them, and it's very common in the breed. It's really a breed going downhill if you ask me. When one is looking at different breeders, they shouldn't just be looking at titles; Some of the most popular breeders have alot of temp issues, regardless of the titles their dogs have. There are very big name popular studs that took years to stand for a judge without freaking out or biting them. A BIS/BISS/Westminster BOB, #1 in the US, etc etc doesn't mean a thing for temperament; A beautiful dog can be trained or forced to stand for a judge.
A friend of mine got a dog about a year ago from another breeder, and she found the dog to be strange and sometimes frustrating to train; In agility, it'd be fine one class, and then the next class suddenly sketchy about every piece of equipment for no apparent reason. Everyone in her class would just tell her "that's just a Belgian being a Belgian -- they all do things like this." NO, they DON'T, and I think it's sad that people think this is the norm. These dogs are supposed to be confident, brave, noble animals; Not shivering sketched out cowards (and if we're talking big titles -- this is a grandkid of the most herding titled Belgian ever (as well as a Ch), and the grandkid of a national BISS winner who also has a multitude of agility, herding, and other titles). Temp problems are hiding in every line; They can pop up at the most unsuspecting times and surprise you; The problem breeders are those who continue to have problems, use those problems in their breeding, and don't make an effort to change them because their dogs win.
Belgians love to be active; In the summer time it's typical to see me at the dog beach or dog park every other day (of course atm with no vehicle my dogs have been homebodies!). I find the dog beach to be easier because the dogs can be distracted away from other dogs; Belgians have a style of play that other breeds don't always understand. It takes a special Belgian to play with other breeds and be accepted as another dog and not some wild thing. There's my male who really enjoys playing with the other dogs and does well. There's my puppy who has gone a few times, but the last time did not show any interest in the other dogs; They mostly just bothered her. She would turn up her nose at them and greet the people happily. And there's my older female who I don't bring. She has never shown any signs of aggression, but she brings the stress level of the park up. She wants the dogs to chase her, and so she's run, and run, and run.. No one can catch up to her, but you can feel the stress level rising. Plus, if toys are being thrown, she tends to steal them, and I don't trust that she wouldn't get posessive if a dog were to try and take it away. If you want a dog park Belgian, you have to start them young and keep them in line.
You can find Belgians in every single sport venue. Agility, flyball, rally-o, obedience, schutzhund, carting, etc etc. There are even dogs titled in weight pull. They are very versatile dogs.
Most of my Belgians have been very dominant dogs. They have a tendency to fool you into believing they aren't if they are soft-tempered. Soft dominance is the WORST. I like hard tempered and easy going, but I find this to be the most difficult temperament to find, even when breeding these dogs. I want a hard tempered dog that can withstand pressure from me and it's environment. If a dog breaks down from pressure, what kind of working dog is that? However most of the Belgians I meet have this problem. Even pure working lines are not immune. I want a dog that can be asked to do something again and again without feeling the pressure.
Really Belgians can vary SO much from line to line and dog to dog, I always recommend people to talk to many breeders, ask about other breeders, talk to people who've bought puppies from different breeders, and try to meet as many dogs as possible. Learn what issues are in the pedigrees. Belgians are a "relatively" healthy breed; Meaning they are healthier than some others. They certainly have a huge issue with epilepsy. Not every breeder is going to be honest about producing seizures, or where the problems lay in their pedigrees. I've talked to breeders who say "I don't know why everyone thinks my stud has an issue with seizures; He's ONLY produced it 3 times." Sorry but if they carry the gene, they carry it. Research is showing it's most likely a recessive. No test available yet, but they're VERY close to having one in Finland. There are also breeders who blame the opposite dog for all of their problems, "it wasn't my stud, it was their bitch." Takes two to tango! It's hard to find pedigrees with an epi producer less than one or two generations back; I try to keep them 3 gens back, and thus far I've always managed that, but I won't be able to do it forever. You have to balance quality of structure and temperament with risk for health issues. When a breed doesn't have a test available, you have to take a chance now and then, or else you'll be like some breeders out there who keep inbreeding on the same lines that they feel are the only "safe" lines (there are no "safe lines").
RE different varieites; You can get tervs out of groens, groens out of tervs, recessive black and tans, tervs or groens out of mals, black mals out of coloured parents, etc etc. You can also get dilutes like blue and liver (most commonly seen in mals). Some breeders are very against using groens who carry terv, etc. Most are pretty casual about it these days. Alot of breeders are excited about the prospects of tervs in a groen litter. It's just something different and new. I prefer my blacks to be black, but with the amount of structural issues in the tervs these days I think it's great for tervs to be born out of groens that can be used by terv folk (rules-wise between clubs it depends on the situation, where the dog is, what it's registered with, etc).
Structurally we are losing shoulder angulation (and thus good movement). I was really disappointed by the pictures of the national specialty this year. There were only a handful of dogs that I thought had an excellent sidegait. The reach in most of the dogs' movement was not even adequate if you ask me. Shoulder angulation is important to dogs going into performance sports and I always recommend breeders that consistently produce good shoulders. We're also seeing ALOT of toed out/cowhocked rears. In fact I rarely see feet that point straight forward. If taking a long ruler and placing it flat along the dog's knee, it should go inward and rest in the dog's armpit. Most go outward. This can also leave dogs susceptible to issues, and the worse it is, the more likely the dog can't single track. I see more Belgians that can't single track than those that can. Single tracking is the most energy efficient way of moving. This is ideal for a herding breed. Too many breeds are tryign to breed them so square that we are losing angulation among other things.
Luckily this is a breed that is lighter than most, so when doing performance sports it isn't going to take impact quite as hard; Therefore structural issues aren't quite as terrible as some other heavier breeds. I see some pretty bad structure out there doing agility though and I feel bad for what the dog must have to feel in it's older age.
Bottom line is, this is supposed to be a confident breed who can do it all; Loyal to it's owners (usually more of a one or two person dog though), protective, intelligent, affectionate... With good health and excellent structure. To find all of this, it's important that one does alot of research on where they get the dog. Some breeders focus too much on one thing and not the whole picture! These dogs are awesome, fun companions, with really interesting personalities. They are different, beautiful, they love to be with their person.. But certainly can be challenging, and not for everyone.