I have both a 450S and a 350ES, and if there both sitting side by side it depends on the task at hand as to which one I choose.
Trail Riding, Rancher Handles better smoother ride responds better to driver input.
2 Up riding, Foreman has more room for 2 people and Handles the extra weight better.
Mudding, Toss up to me the Foreman has more power and heavier so then it sinks faster.
The rancher is more driver friendly and responds to driver input faster than the foreman.
The Foreman will outwork, Pull/Haul/Tow the rancher.
it will depend on what your use for the 4 wheeler will be.
A mostly trail machine with some work Rancher
A work Machine that gets out on the trail sometime Foreman.
If I could only have 1 it would be Foreman I due 70/30 Work/Play with mine.
if I was 30/70 Work/Play it would be the Rancher
Work I due is Skidding Logs and pulling trailer's full of Wood.
The Rancher is adquete and more nimble driving around trees but the Foreman can pull a bigger log than the rancher.
just my thoughts sublime out.