I can't think of too many in game pets off the top of my head, there isn't much variety there unfortunately.
There are some ok event pets, sissy cello 90 and mischievous poppuri 100 look alright for gunners if you can find one of those.
Far as myshop pets go, I would look into a power based pet as they tend to have higher ac than sense pets. Power pets also give hp and hv which are nice for a gunner to have due to lacking a shield.
Just to compare, here are the wiki pages for the 130 power and sense pets:
Mars - ggFTW Trickster Wiki
and Mercury - ggFTW Trickster Wiki