Long answer:
The GTS and the PRO are priced quite similarly but are quite different in performance. The pro and ultra are simply overclocked versions of the GTS. Normally the pro should be priced closer to the ultra than the gts. In truth, the ultra is clocked high enough to need a bit faster memory which eats into profit margins. Card makers have deliberately lowered the cost of the pro to encourage people to buy it instead of the ultra since the profit margins are so much better. As a result the much better performing GeForce 2 Pro is priced about the same as the GeForce 2 GTS.
the pro performs quite well...
and with the ddr memory, it can handle higher resolutions...
the mx series isnt quite as fast, and uses sdram, to my knowledge...
get the pro...very good deal.