I mowed commerically for a few years and had a chance to run several different types of zero turn mowers.
I currently own a Dixie Chopper XG2703. It's 27 horse power, with a 60" deck. It is about 4 years old and has about 450 hours on it with no problems other than a broken drive belt, to date, knock on wood. I mow about 4 or so acres a week currently. Dixie Choppers are made in Indianna and are not as big or well known as some of the other brands. What I like about the Chopper is it has a bigger hydraulic fluid resevoir than other brands, at least when I bought it. It has a 1 1/2 gallon tank, when the others have around 1/2 gallon hydraulic tanks. It also has a hydraulic oil cooler. This is very important because when the oil over heats it has a tendency to burn up the wheel motors which are very expensive (500-800 bucks a piece). Also, if you develop an unnoticed leak while mowing, you have more of a cushion before you burn your wheel motors up also. Look for the bigger wheel motors also, the bigger they are typically the faster you can go.
I like the 60" deck because it is big enough to cut your mowing time down but it doesn't scalp that bad like the 72's tend to. Look for a deck with welded seems, not a pressed deck. The pressed decks get thiner in the corners during the forming process and tend to rust out alot faster. Blow your deck off after mowing, don't let the grass sit on the top of the deck it will rot out alot quicker.
I notice you said you had alot of trees and if you buy a new mower it will have rops and these things tend to get caught on everything when on a zero turn, so be careful. I nearly killed myself one time when I caught mine on a powerpole guide wire.
If ride is important Ferris has mowers out with spring suspension to help with ride comfort but I have never operated one.
If you get one, it will take some getting used to but after you get the hang of it you will love it and cut your mowing time in half. As your turning remember to turn your inside wheel backwards a little if not you will tear the grass up. You'll get better with time in the seat. Be CAREFUL on hills and around drop offs.
What ever you do buy the mower with best hydraulic system and the biggest motor you can afford, you will be happier in the end. Keep it serviced and you should have minimal problems.
Hope this helps. Good luck!