You will get more travel for the same or less money and get a lighter bike if you buy a 26" FS instead of 29er. In return all the 29er offers you is increased tire volume, which is indisputable, and 'better rolling' which I have personally not observed.
To answer the thread title question, the answer is very obviously full suspension of some kind. I see that sentence about rocky endurance races. No doubt full suspension. I doubt there's a better bike under $2,000 than this one:
http://www.speedgoat.com/Catalog.asp...t=1&Prod=23844 (most sizes are $1699, and I bet all of them will be very soon.)
If you want an upgrade and a 18-19" bike fits you, get this instead:
http://www.speedgoat.com/Catalog.asp...t=1&Prod=23841
(BMC's bikes tend to run big. This one is no exception. It's a very big "medium".)