KT266A by far. KT133A is a dead end, and really there is quite a difference between 266A and 133A. AMD 760, was a great platform in it's day, but it trails KT266a by a bit, especially in memory performance. Go 266A.
EDIT: Also, I would not recommend 760 because it is just as stable as 266A, and if any thing, you may have more trouble depending, because 760 boards use the notorious VIA 686B south bridge while 266A uses the new 8233 sb, 686B should be avoided.