What is the best way y'all level your characters?

I really wanna get upgrades for the Z7 Imp and Foot Soldier (and Peashooter and Colonel Corn) but trying to level thru PVP is very demoralizing with how much I get instantly vaporized by the enemy teams' "Piss Pea with a Plasma Cockmongler"...

Do people even play Garden/Graveyard ops?