IMO, for maximum profit - choose Alts in advance, hold BTC, wait for the fork, sell for Alts as soon as possible. I don't see why any active trader would do otherwise. The only thing I have doubts about is that too many people will think this way and so there won't be much profit.

If you're not an day-to-day trader - don't participate in such high volatility events, just hold what you have if it's going the way the way you expect it.