Bunny,
As far as the discussion about the best tractor of the big three, that has been discussed (argued, yelled, screamed) at length here. Most participants are reluctant to say anything remotely disparaging about any other type of tractor. Suffice it to say that I believe that Kubota's tractors are the best engineered, most reliable, durable, functional, solidly built tractor on the market today. They are also priced well compared to other manufacturers.
Size/power of tractor:
The bigger the size/power of the tractor, the bigger and wider variety of implements you can use. The bigger the implment the faster the job get done. I'll repeat that: The bigger the implement thet faster the job gets done. When you first get your tractor, it is fun to mow/hog, etc. After a couple months, it becomes a chore and you probably have better things to do on your weekend than mow/hog for 6 to 8 hours. For your application (as long as your acreage is fairly open) I would suggest buying the biggest finish mower and brush hog you can. As I recommended earlier, the Kubota
L3710 can pull a 84" and maybe a 96" finish mower. In addition, if you were willing ($$$) to move up to a
L4310 or
L4610 you could pull a batwing 120"+ tri-deck for finish mowing.
Transmission:
Gear transmission is less expensive, but you have to shift, change gears and put the tractor in reverse to back up. HST will put all those controls at your foot (like a car with an automatic transmission except you don't have to put the tractor in reverse to back up).
Tires:
There are three types of tires. Ag - most aggressive and traction but will do damage to your grass. Turf - least aggressive and least traction but less damage to the grass. R4 Industrial - Compromise between Ags and Turfs. I would recommend R4s for your application. Also, R4s are more puncture resistant than trufs which could be a significant factor in bush hogging.
FEL:
Something you will regret if you don't get one. I sure did. I had my FEL installed a month ago and it improves the functionality of the tractor by a factor of 10.
Best of luck which ever tractor you go with.