I wanted to entitle this post "2D or Not 2D, That is the Question." However, I didn't think it really said what this post is about so I chose it not as the title, but thought it was so corny that it was worth the mention.
Back to the question, should I learn 2D or 3D animation? I can only speak from personal experience and what I occasionally hear elsewhere, and to cut a long story short, go with the lowest number and work your way up is my suggestion.
Many would-be animators start with 3D, as it is the easiest to initially learn by my reckoning. However, I was one of those who made this mistake, even investing money in a 3D package that I very rarely use. What a waste!
I moved over to 2D animation as I eventually realised that this gave a much better insight into the complexity of creating animations and learning the 12 principles of animation. My intent when I switched to 2D was to learn the basics then move back over to 3D. But, do you know what, the more I started to learn, the more I was hooked. The date for moving back to 3D keeps getting put back further and further, whilst I get more into 2D.