I LOOOVE the whole line. Toys I've tried personally:
Squirrel Dude - an improved version of the Kong. Just dry kibble lasts about 15 mins, stuffed and frozen it can last up to 90 minutes!
Twist n Treat - great toy for stuffing as well; filling lasts a nice length of time, similar to SD. Not as durable, though - some dogs will rough up the edges.
Waggle - one of Maggie's top favorite toys ever. Even after having hers for well over 2 years she still takes a good 30 minutes to empty it of biscuit pieces vs. the 10 that most toys last her. Very durable - Kes loved to try and kill it but hasn't made a dent.
Kibble Nibble - sturdy treatball, but fairly easy to empty. Easy to fill, so great for meals for fast eaters.
Tug a Jug - very difficult to empty. Can be dangerous to walls and breakables if your dog enjoys shaking his toys. The rope (both rubber and cotton versions) can be easily chewed up so this is a supervised use toy imo. Some dogs find it too challenging.
Bristle Bone - very different from the other BB toys. This bone encourages tooth cleaning chewing through the use of rawhide or cornstarch rings sandwiched between nylabone ends and bristled disks. Quite durable and long lasting for most dogs - ends are worn down at about the same rate as nylabones in our house.
Football - one of Z's regular toys. Not too difficult, not too easy.
Biscuit Block - a more challenging version of the Football, so it's a favorite of Maggie's but Z gives up on it. Technically a puppy toy but I got the size larger than recommended for the pups' sizes and it's held up quite well.