Tekken 2 Ver.A - hated the updated AI in Tekken 2 Ver.B as all they do is single punches (pokes) and kick you, and the rising kick they always do hits mid so you can't duck it! System 12 is a bit over-specced for my pre-Core2 museum piece and gives me about 48% in the non-interlaced 512x240 mode of Tekken 3/Tag; Tekken 1 and 2 at least get 60-70%.
With Mortal Kombat, I couldn't stand the lack of a run button in MKII (and MK1), and the fact Shao Kahn was a bit too overpowered (e.g. 3 charges through your moves/rope/ice etc = death in 2 seconds). Definitely a MK3-era player, that is when the CPU doesn't decide to go into 'cheat mode' (which was designed to take your money in the arcade so you'd quit in disgust).