IMO, the MP5 is a great upgrade from the MP7. Now, maybe its because I joined during the christmas event, thanks the free weekend thing, but I like using the mp5 because it basically gives you 3 healing darts at once, where as the mp7 only gives 2 darts at a time. Being a lvl 6 medic, the recharge is amazing, but it sucks being able to ony use two healing darts, because people keep moving randomly, and sometimes lag makes it miss, or even the fake green puff makes me think that i hit the palyer, when actually, I didnt.
As for the other weapons, I only know that the claymore is a nice substitue for the katana/axe pair. Ive used it a few times, and although its a slow hitter, it works well with my lvl 4 zerker. However, I would never use the claymore as an off perk weapon. Too slow, weights too much, and doesnt fit any of the other perks that well.
Husk cannon, I just dont feel like its that good at all. yes it has charged shots, yes it can fire long distances and even stun husks, but its easy to chew through the ammo.
And as for the combat shotgun, its very useful for soloist, but in groups, its too easy to waste shots by accidently firing more shots than what was nessacry.