Exo suit or FRV?

I as a fan of liberty donator in the heaviest of machines need to know in wich machine i'd do it the most liberal way.

I am a Halo veteran and i loved the Warthog drive by gameplay. I play with 2 buddies. The FRV seems to be exactly what i look for, but all the videos i saw mostly ignored its gun platform and chose the sideseats to use bigger guns. So my real question is, should i get one of both mechs first instead? I love big guns (the AC-8 Autocannon is my favourite gun in the game). Thats why im torn between fun and potential inefficiency or being a damn mech walker but walking on my own