That is not so easy a question to answer. There are several variables you need to consider.
1. What size, HP, tractor do you have? How wide from outside to outside of rear tires will determine width of tiller.
2. Do you want a chain drive or gear drive? Check back there was some good responses to this issue in a recent previous discussion here.
3. Parts availability and warranty.
4. How big an area are you planning on tilling? This could impact model, price, etc.
I have a 48 inch Caroni FL1200. I use it on a compact tractor and the FL1200 was designed for 15 to 40 HP. It does an excellent job. It is a chain drive, weighs 408 lbs so it is heavily built and sold by AgriSupply. They have very good prices. They keep parts for all their equipment in stock and are the most customer supportive of any company I have dealt with in recent years. They sell a more heavily built tiller that is also a Caroni and they sell King Kutter tillers. Please keep us posted on your selection, why you chose the one you bought and how you like it.
A blip from Agrisupply on my tiller:
Ready your orchards, gardens, and vineyards with this compact Caroni FL1200ASC tillovator. Suited for tractors with 15 to 40 HP, this tiller includes 5 discs with 6 hoes each, equaling up to 30 tines in total. It also has a standard adjustable hitch and universal joint with clutch to quickly and easily attach to any towing tractor. A third floating point allows for a 6-1/2 in. displacement to the right in order to keep the PTO shaft aligned. Made out of high quality materials, this 48 in. rotary tiller is ready to work on a variety of terrains.