There's no such thing as a "good" pump group. It's only good if you're actually the owner and the one making calls/signals. Before the owners/admins pump a coin, it's almost guaranteed that they've stocked up beforehand, so they can sell on the way up.
Exactly, pump groups are essentially just groups of thieves, I had been invited to join a few and always refused. It's essentially stealing from others and there's no justifying it, regular trading is completely different.