By far and away Id have to say FroggerNG. Moovid I found more or less useless, seems to work with maybe 1 in 10 avi files, while froggerng plays probably 90% or more of my video files (including HD mp4 rips surprisingly). Really though if you want to deal with industry standard video files on a 68k machine Id advise to use MPEG files due to them being less hardware hungry (although I assume there's a reason you specifically asked about avi's?).
