they are all the same in terms of performance. the pro is white and dose not come with a hard drive to save your games to whereas the elite is black and comes with a 120 gb harddrive and one month of gold membership. if you can find an arcade that comes with like 128 mb of memory or something and is white. its mostly just what color you want.
then you have some special edition elites what come with a free game promo, like the resident evil 5 box was red, halo 3 was camo green, mw2 is black with silver logos on it.
Buy the ones that were released after 2007 or in 2009 would be better because the new versions like the elite version would support 1080P with HDMI port and Microsoft also fixed "the red ring fatal error" which is the common problem that many customers encountered with the versions that were released in 2005. So try to avoid the older 2005/2006 versions.
For the PRO version, I am not sure but if it is recently released or still being new then I think that would be just fine.