People swap to the Gnasher out of spawn because that way they can pre-active and thus ensure nobody else has a chance. It's as bad as the retro.
Personally, depending on the size of the map I keep my Hammy out. If its a mid-small size map however, I'm bound to end up being rushed by some rambo f*ck-nugget who thinks he's God, and seeing as the hammy has been nerfed so far that retro's out class it at long range, I'll keep the Gnasher out. Or Sawed-Off if I feel like trolling said players.