You'll be able to fit an auto diff from an automatic to help the gearing. E36s are probably easier to build as parts are more interchangeable on them with other models compared to E46s but they can still be made very good skidders too.

Diff ratio, coilovers and getting rid of the shitty DMFs is the three things that will make the biggest difference to an E36 or E46. Same goes for E30s of course but just steering rack rather than the DMF.