I decided to go with the 12.9" for the first time since it's supposed to have a lot smaller footprint as well as being slightly thinner, which means it should also be lighter. The new one, including the bezels and all, is supposed to be exactly 8.5x11". The 10.5" is fine, but when I have used the 12.9" I like it so much better. It feels more like a computer and has more space for toolbars and things in editing and drawing apps, as well as full sized app multitasking.
Not sure if we're getting an 11" in the same size case or 10.5" in a smaller case. I was leaning towards the former based on rumors and what I think makes more sense in the product mix to separate it from the 9.7", but if it does go up to 11", then that could be a good option that has a bit more space for you without being so big or expensive. Also note that it's likely that the prices will go up this year. I would be pleasantly surprised if it's less than $100, but $50 is a minimum and $100-150 is more likely. We will know all the answers soon enough!