RealVideo is usually best for data rates below 3 KBps.

It works better with relatively static material than it does with higher action content and usually encodes faster.

RealVideo 8 vs RealVideo G2
The default RealVideo 8 codec results in visual quality markedly superior to that of the RealVideo G2 codecs.
It requires more processing power, though, so encoding a clip with it takes longer than encoding the clip with a RealVideo G2 codec.
RealPlayer 8 and higher can play RealVideo 8 clips. Earlier RealPlayers attempting to view a RealVideo 8 clip are prompted to auto-upgrade to RealPlayer 8.