I've noticed that there are generally two broad types of accounts that brokers offer:
(1) 0 commission, large spread
(2) $3-$4 commission, tight spread
So far I've been going for (2) to try to minimize slippage; my main concern was trades not getting copied if the price difference was too high.
In some cases, however, account (1) seems to be a better deal (cases where commissions are too high, leverage is too low, or min deposit is too high), so I'm actually now revising my conclusion that (2) is better for copy trading to make sure I'm not missing something.