hey peeps thought id start this as aint seen much on the upgrades, and whats worth the dosh and whats a total waste of time an effort. dont really consider this as any kind of spoiler cause it doesnt really refer to any plot points. obviously ill assume ya got all the stuff ya can get by doing the story mode and side missions.

guitar strings: the ones to max shocker range and power, as means ya can do damage to alot of enemies before they even lay a slimy paw on ya and totally wrecks the vehicles
axe: the leechy one that heals as ya whack. means you can open the can of whoop ass for that wee bit longer before ya gotta run off squeeling an hide lol
deuce primary weapon: honestly the normal rocket. it seems to have a decent range, ability to lock onto targets (unlike another 'un which consistently will fly over enemies heads which really makes me blood boil), and unlike alot of weapons will actually stop your enemy attacking most of the time.
deuce secondary weapon: the good old flames, cause ya can just plough thro the enemies and those ya dont smack with your bumper, ya'll usually set on fire (which totally knackers the grave diggers) and ya can then proceed to reverse back over them again with the flames still on. mucho satisfyin

strings-max shocker range/power fo sho.although the ones that cool faster are good too.
axe-steel quilled blade,or if your too lazy to beat all the hunter missions,bloodlust is awesome.
deuce primary-lightning shooters,awesome power range and accuracy.plus it looks the coolest xD
deuce secondary-sub woofer.owns anybody around you and it charges fast.in short,it gets the job done.