If you can do agility, obedience is way easier lol. And rally is pretty easy too. If your dog has a decent loose heel it doesn't take much to teach the few moves needed to get an RN.
IMO competition obedience is actually harder than agility IMO. It requires more focus for a longer period of time. Rally it depends, Rally Novice is a very entry level title but it depends on what you want too. If your only goal with obedience is a RN, BN or even an RA and you don't care about scores, you can definitely get by with entering a dog who only has a "loose heel" and knows some basic commands. If you want to pursue obedience though and train to a high level of reliability, entering your dog before they really understand heel will set you up for problems down the road. I see this at the training club when people think it would be impressive to put RNs and BNs on their 6 month olds. The dogs get the titles but once they move to Advanced and/or start working towards a CD, it becomes painfully obvious that the dog has little concept of what heeling is and obedience work becomes a struggle for dog and owner.
I enjoy training competition obedience, specifically training focused heeling. I don't find it any less interesting than training dogs in agility or tricks or flyball or any other venue. I find people who do obedience and have the opinion that it is "boring" for the dog, especially at the lower levels tend to have dogs who aren't well trained in it - they reflect their owner's attitude
If you aim to train for focused heeling, I don't think you or your dog will find it boring. If you go to group class where the 45 minutes of the class is "heeling" consisting of walking around in a circle with your dog, you and your dog might find it quite dull.
This is my "puppy" at just under 2 years old getting her RN title - complete with handler error
I've used Rally as a way to get her into the ring before she's ready for a CD and be able to offer help with the areas she isn't solid on yet - circles and finishes for example. But her overall understanding of heeling is pretty strong and that is a large part of what the Novice level obedience is (Rally and competition OB).
YouTube - Whimsy Rally Novice New Title 12-19-10