I've tried several commercial softwares, free converters, everything else including WinAVI (which gets a letterboxing since the res isn't exact).
WinFF is as fast as WinAVI, gets the res exact, lets you customize all the parameters, and even allows 2-pass encoding for the highest quality possible (you can reach Youtube .flv file sizes easily while maintaining quality).
On my Sansa e260 Mpeg decoding only goes as fast as 20-21 FPS, otherwise it has to frame skip a lot to keep up, well now you can restrict it to whichever you feel (I use 15-20) because other converters don't allow under 23/24 FPS and some get errors even if they support it and you try. Now I can leave frame skip off, and if I display the FPS it's at what it should be, and if I don't limit the frames it actually goes a few fps too fast for the audio...
I haven't done extensive testing, but the quality, features, and ease of use are all 100% excellent.
Test it out and see if it works pretty good for you. Click options for the advanced parameters.
Set it to "Convert to: ......." "Device Preset: RB __________ (ratio)" and select your output folder
Update: It works perfectly with 2-pass, 182kbps video stream and 112 kbps audio @ 224x176 mpeg-2 means a 20 minute 42 second episode can be compressed to 46.8 MB without too much loss of quality.