I would probably say the first generation G3s, the 233MHz machines. Some of the earlier models which use 604s are also similar performance wise: PowerMacs 7300, 7600, 8500, 8600, 9500 and 9600.
This is based on my experiences of these machines and 700MHz-ish PIII machines.
This is based on my experiences of these machines and 700MHz-ish PIII machines.