Depends what era of Factory fare you wish to refer to and what you are looking for in handling, sports or touring car.
There used to be a different Morgan model for every taste in driving. They were far more distinct from each other than they are now. Presently, all trads are built on the former Plus 8 chassis, so the weight and handling characteristics are close to identical..save for the power factor and, of course, the price. So if you are speaking of the present Plus 4 and the last Plus 8, you are simply asking whether a bigger engine makes handling easier or harder than a less powerful engine. Easy answer.
However, if you compare apples with apples, I think the new Plus 4 (with 155bhp) is the best Plus 4 ever, outside of the sublime Plus 4 SS.
If you speak of the days of yore, for me, the standard Plus 4s were too heavy to have the 4/4s lithe joyous agility and not light enough to come near the Plus 8s muscle-assited handling. Power can get you out of trouble as much as it can get you into it. With that in mind, the sublime Plus 4 SS was surely the most together car the Works ever made in every way.
The most versatile handling combo is always very low weight and lots of power, whether you wish to go fast or slow. The best handling all-rounder from the MMC I have driven to date was the first MMC proto-type V6 designed by Bill Beck, then in charge of the Development Division. It had the Lincoln Continental version of the V6 in a super light 4/4 chassis.
Lorne