I don't think there is only one size of either of them... there must be a "small" and "medium" size for most Bamboos, so just look up the specifications and what it says about the active area size, and you'll know for sure.
Personally, I'd go for a medium size definitely, it's more comfortable to use. I think that's the best size for most people. Large may be too large (although I love mine, some people might find it too bulky), small size is OK for a start, but I always advise people to save up for the medium size instead.
I don't think a larger active area seriously matters. I've been using a bamboo pen for a year now, and it works perfectly fine. I've also started using Intuos for classes, and it doesn't make much difference. I suppose it all comes down to personal preference.
I'm not sure how big Bamboo Create is compared to Intuos though.