I went with the Femco Tuff Top on my tractor and my lawn mower. It's a softer plastic top that you assemble yourself. I've hit more branches with it then I can remember, and it just flexes a little. I've found that the shade makes it a lot more comfortable on really hot days. It's a significant difference!!!
When searching for the best price, I found Rural Kind to be the best at the time I bought mine a few years ago. I don't know if they are still the lowest price or not, but if I was to buy a third one, I would probably just order it from them again.
Femco 48" x 52" Tuff Top Canopy 32221 : Rural King