Smash4's theme is the best concept yet, however the worst execution of the concept, in my humble opinion. The first time I heard it, it was incredible. It's energetic, so it's easy to see why you'd like it right off the bat. Especially the way it starts, those powerful drums building to a pretty epic moment before the main melody starts. Then the lively, "adventurous" section starts and the orchestra sounds so full, it's truly vivid the first time around. Even the second, and third, and so-on.
But eventually, you reach a point where I'm at now. The point in which you realize the music has no flavour. There's no growth, nor decay. No ebb and flow. It's incredibly one-dimensional, everything happens on the same level. I don't mean dropping the energy/"bounce" the music has, that's all well and good, it's just the mixing and general lack of dynamics the music offers that I find irksome. It's all so blasé.
Now, I did say I think it's the best concept, and I truly do believe that. I think the arrangement of the music and instruments is incredible, only the execution of the song as a whole is somewhat underwhelming. Nothing stands out.
If you had asked me this a couple of months ago, I wouldn't have said that. I would have said "Smash 4's is the best, hands down!" Now, however, I'd rank Brawl's theme at the top. It's lovely, and the orchestration actually has feeling to it. It's dynamic. Am I biased? Certainly, as a singer I'm more likely to appreciate operatic styles than the average person. But it is what it is.
Smash 64's theme is incredibly erratic, although an actual theme for that game is somewhat... unclassifiable. I'm talking about the opening cinematic in this case, and I just find it strange. It really just pops around all over the place, and sounds really harsh. I can't say I care for it.
Conversely, Melee's theme (Menu 1) is incredibly stale, and, frankly, boring. I think I don't care for it simply because it's all just recycling the same one theme. Sure, it's played differently in different sections, but none of it even feels very different to me. Menu 2 would have been a far more suitable theme for that game, at least it was interesting. Unless you want it's theme judged by the music used for it's opening cinematic, in which case Melee's is very, very good. It also lacks dynamics in certain places, but I suspect that's more intentional than the case for Smash4, given this music was composed with the intention of being behind the cinematic, (i.e. it compliments the video, doesn't intentionally take focus.) I'd probably be amazed at how gorgeous it is if I heard it from a live orchestra.
I suppose if asked to rank, I'd say something like:
1- Brawl
1.5- Melee cinematic
2- Smash4
2.5- Melee (Menu 2)
3- Melee (Menu 1)
4- Smash 64
I guess this is all my opinion. Take it as you will.