I used Xilisoft DPG Converter (it's a paid app, $20) with settings of:
Resolution: 256x192 (Fullscreen) / 256x144 (Widescreen)
Bitrate: 800kbps
Framerate 12 (Animation) / 15 (Live action)
Sound bitrate: 128kbps
I haven't had any issues yet. Have converted both 30min long eps and full, 2 hour movies.