Act 1 and the stock player are the only ones I've tried so far, but I love Act 1. The stock player always struggled controlling the movie files I made, trying to scrub through the movie was choppy and navigation was very sparse. But Act 1 has silky-smooth scrubbing, great customizable interface elements(time elapsed/total time, battery status, time), and slick touch control(touch center screen to pause/play, lower right for brightness, lower left for progress bar, etc.).
I've not had much cause to search out for any other better players.