Depends what you mean by AVI. Capturing to a lossless AVI (huffyuv, VLBE, etc.), then converting to MPEG2 should give you better quality if you use say CCE to do the mpeg2 conversion and do a multipass VBR encode. I mean try doing multipass on the fly. Also means it is possible to do some filtering to remove noise, etc. if needed.
If space and time really is not a problem then you could capture multiple times and merge them. This helps to reduce analogue noise (at least in thoery).