200 is no easier to service than a 300 really.
the 300 is better to do the cambelt, as you don't need to drain the coolant system down (or disturb the water pump)
300 (as stated above) is slightly quieter, but by no means silent.
the 200 will drop in where a 2.25/2.5 4 cylinder used to live, using the same chassis mounts and fitting pretty much all the 4 speed (series) and 5 speed (LT77) gearboxes.
300 will need different chassis mounts (PM me your email and i'll send over all the dimensions for them) and (to be a "factory" install) an R380 box, although the LT77 can be made easily to fit the 300 (Read about it all here
My preferance is the 300.