This is my top 10;
S: genfu
A+: Leifang, Ayane, Christie, Hitomi
A:Jannlee, Hayate, Helena, Akira, Momiji
Requiem has genfu, Christie, Ayane, Leifang and Jann lee as his top 5.
EDIT: Some reasoning about the change in letter grading and some things I said earlier in my previous post. DOA5U is a very balanced game. Unlike a game such as SSF4 AE (which is also pretty balanced), character match ups have a bigger toll from top tier to say mid tier, and low tier. Some or most match ups are either favorable or really difficult for some mid tier characters versus a top tier (always depends on players of course). Thus they have SSS, SS, S, A, etc etc.
DOA5U does not have any character in the game who just flat out wrecks the cast. DOA has characters where everyone can actually fight someone else pretty well, or well enough. No one is broken or overpowered, some just have the ability to shift the momentum in their favor more often than others. While some also just seem to have better tools overall than most. That's why the letter grading starts at S, and the next is A+. In my honest opinion, I do not believe any character is terrible in this game. So I do not believe there is anything below C, which describes a character being awful if they are in D or F.
Certain characters I said were possibly top 10 earlier are not in my top 10 because I re-evaluated them and other characters who are in it. Most would think Momiji doesn't really have a lot going for her, I urge folks to look again. I also believe that Akira is the best virtua fighter character in this game compared to the other three. Who are all generally pretty strong anyway, but I don't see Sarah being any better than Akira at all.
Having frame traps and good frame advantage is always a good thing to have, but it is not the end-all-be-all of DOA. Defining practically the entire rule set of DOA is what makes a character outstanding in this game. This game has a heavy influence on environmental interaction, and the top 3 take huge advantage of that aspect, which is one reason alone why they are above everyone else (lots of characters take advantage of that but some have the ability to do it from almost everything they do, more than others).