There are a lot of good zero turns on the market. Scag makes great mowers. We run Kubotas. A ZD 326 Kubota with a 60" deck is a beast. Our operation is brutal on mowers and ours has had no down time in 350 hours. We are going to have to changer the deck belt soon otherwise put fuel in, service at regular intervals, cut grass. When we trade mowers the only thing I will consider will be Kubota unless our clientele changes drastically.
There are many mowers out there that cut great. I have not looked at any that appear as rugged as Kubota. They are built like tanks. We also have a ZG 222 with a 48" deck. Only regret on the ZG 222 is that I did not buy the ZD 221 instead.
The jury is out on the 100 series mowers as far as I am concerned. Course they are not really commercial mowers anyway.
I have seen a lot of commercial guys replace other brands with Kubota. I personally have not seen anybody in our area replace a Kubota with anything else.