I vote for Shizuru- because he is a stupidly fast player, not just for mouse only. He has one of the best HD/DT of anyone regardless of the tools he uses. His replays are impressive before you find out he is mouse only. He's not quite top10, but I would say he could be top15 or 20.
Also some people say that cookiezi didn't play enough in 2012, but he had PLENTY of impressive scores in 2012 that put him atop the hill. He played enough at the start and end of 2012 and showed that he didn't need to be playing all of the months in between to prove himself. He played the first and last three months of the year and then took 6 months off. During those two periods he did big black (not beaten from the time he set it until 1900 plays from rrtyui a month or so ago), SS'd airman, freedom dive, rainbow dash, ect. If he can take 6 months off playing and come back to take rank 1 within the week and begin to stomp on everyone's scores like it's nothing, then he's the best of 2012. He ended the year on a terror, and is still going.
People like SilviA and Remilia, though, I understand being left out. They haven't done much this year, despite all they did in 2011. They are still amazing players, but haven't done much with their sporadic and limited activity. Others have out-shined them, so it makes sense to leave them off and recognize those who are still posting scores.
Also, making a top15 is hard. Lot of good players can be considered for the 5 spots that aren't cookiezi, niko, rucker, ww, rrtyui. Only a mere10 spots to sort out who makes the cut in an ocean of talent. Way more than 10 other names could be considered deserving of a spot. Will be interesting to see how it turns out!