Nier vs Parasite Eve - Uh...yeah. Parasite Eve's got a good soundtrack, but I feel Nier's fits a lot better. I've never been thoroughly impressed with PE's soundtrack - I feel it is somewhat poorly utilized in-game - but it's good. Nier's is just better, and a heavy vocal soundtrack works pretty well for the game.
Iji vs Wild ARMs 2 - So...uh...I like a lot of the WA2 songs. I think Battle with Lord Blazer is a bit overrated, but still good. Just...I remember all of 2 of them. I think the repetitiveness of the music might be the problem. Still, though...it's good, and fitting. But it sticks with you like Chinese food - just in and out fast. And while a lot of the songs are good, some of them are...not great. Honestly, I am not a fan of most of the battle themes, and many of them get underutilized. I think this overall reduces the cohesiveness of WA2's OST - you spend so much time in combat (bosses or otherwise), but the music is so underwhelming. Iji...seems to fit a bit better based on my research. The music sticks with you better, and generally feels more cohesive. And now, having started to play it a bit...yeah, it dominates here. Perfectly fitting, excellent style, etc.
Actraiser vs. Higurashi - You are a god. Kick some ass. It fits.
LoM vs BoF5 - Good fight here. I honestly think BoF:DQ wins this handily. The overall feel of the soundtrack is much stronger - it really makes the world come alive. LoM...does the same, but nowhere to nearly the same degree. I like some songs in LoM a lot (the ending vocal, some of the unique battle themes), but those are all I really remember about the world. BoF5 continuously gives off the air of a dark, awful world, and the journey to a brighter future. Cohesiveness and overall fit is stronger with BoF5.