ES stands for electric shift. EPS stands for electric power steering. So you have a Rancher 420ES with EPS.
If yours is 4wd, when you are looking up parts, the correct name for yours will be Rancher TRX420FPE.
TRX = Fourtrax
F = Four wheel drive
P = Power steering
E = Electric shift
Honda can be confusing with all their different letters.