SM58 LC : THE live mic standard for a reason.

I've seen people use cheap SM58 look-a-like mics on stage and they have no end of problems with feedback because the cheap mics just don't have the frequency response of a real SM58 they have to up the mid and highs at the desk thus causing their mics to squeal like little piggies.

You don't get that problem with an SM58. Not only are they built like tanks and will survive your lead singer throwing one on the floor in their typical diva-esque rages over and over again, but they just sound great. Full stop.

I've never had a problem EQing an SM58. Not once. Plenty of problem EQing cheap look-a-likes though, so don't waste your money. Buy a proper road-tested SM58. You won't regret it.