I would look at the big three to begin with (Deere, Kubota, Massey) and see who they compare in prices. Each one is comparable, so comfort in the seat and dealer service is going to be a big seller.
As far as tires, turfs are actaully tuffer than ags. Ags will give you better grip however if you are going to be on people's lawns and are planning on getting MFWD, then turfs should suite you well.
HP is all going to depend on how big a brush hog you will want to run. Weight is what makes a tractor pull, but hp is what enables you to run a 6-7ft hog.