Honestly for 30 hours a year the Briggs will work just fine. You are putting no hours on that at all. Just keep the oil/filter changed once a year and you will be good for years.
Does the leftover machine with the FX730 have the iCD deck on it? The 730 was rated at 26HP before the change. Its more than enough power.
I would say if you want the latest and greatest get the Briggs. If you feel better about a more commercial engine and dont mind the leftover machine go with the FX730 machine.
We sell Ferris but most of our Ferris customers are homeowners buying large mowers and for them the Briggs is a good choice. I am not a fan of selling them to a commercial guy but on the other hand I can sell the 30HP Briggs Cyclonic for about $1000. Blow one up, put another one on cheap. A 30-36HP Vanguard would run about $2500.