I will continue with the other 2 formats out there that are also used.
MP4s are almost as versatile as AVIs though they can suffer more glitches and mistimings. Most can only be hardsubbed too. With that they can have better quality sometimes and sound can be clearer. However if you back them up onto a DVD or VCD they won't play on a DVD player.
RMVB/RVB's are similar to FLVs in which they can be smaller in size than an AVI or MKV but unlike an FLV, if done right, it can have better quality. The downside is not many players can play it, can only be hardsubbed, and it will sometimes freeze. it will also not play on a DVD player if burned to a disk.
so AVI > MKV > MP4 > RMVB/RVB > FLV