MK2 all the way. Even a DX7s is much better than a MK1. Sound differences are so minor, but 'clean output', backlit screen, unison mode and better buttons/better menus are much more important in day to day use.

Have had 4 DX7 Mk2s (3 'S' and 1 'II-D') - personally i'd advise an SY77 which CAN sound just like a DX7 II if programmed right (and I've done this myself to prove it TO myself). But a DX7 is cool regardless.