Optimum video codec for low end Android phones?

While I know Android phones play mp4 the best, I wanted to know what other specification in this container is the best for playback, (the bitrate, resolution, fps etc). Or perhaps some other codec/format that Android can (or is designed to) play smoothly and with an acceptable file size/quality ratio? I searched the Android developer page and tried the H.264 setting on my converter etc, but the file fails to play natively on my handset and when I tried to open it using RockPlayer. It plays slowly and the video-audio gets out of sync progressively. I tried many external players. However, 3GP videos from my Nokia phones play smoothly (even natively). **So I want to know what is ideal for my low end phone (video should be normal quality and size)?** My phone is a Huawei IDEOS U8150 running Froyo with a 320x240 resolution and a 528 Mhz ARMv6 processor. Also if anyone has tips, what types of encoding is recommended, if I'd be using the software decoder mode in apps like RockPlayer, so I can achieve more file size compression yet achieve smooth playback?