The hot rod Chomper has always been very popular and can work very well if you have gotten super sticky goop from the sticker packs. If you play it well you can get big streaks and really annoy the zombies.
The fire Chomper also works really well in close quarters with sticky goop as its spray can do massive damage to multiple targets. It's great for defending objectives and other things.
Yeti Chomper can work but it can be a bit difficult to use as its projectiles have a strange arc. It's good for killing AI zombies but you get more assists compared to kills in multiplayer game modes.
Also try using the Chomper class on the seeds of time gardens and graveyards map. I remember when I was new to GW2 there was a stealthy disco Chomper who stayed behind us the whole game and killed us constantly as we spawn via portals.