It's going to depend on your budget.russianstang said:
Griggs makes the best, probably, but it costs a ton to install, and you lose your power seat.
I personally like Kenny Brown's, specifically, they are scaleable -you can purchase the system in pieces and install as you have the time AND the support the seat area. Once in, they are nearly as rigid as Griggs's.
Scott Hoag uses 'em too, but KB's shop is closed. You'll hav eto do some hunting to find them . ..
As for the rest, Steeda has the seat braces like KB's, which will support the floor, and are cheaper.
make sure you spec the clearance, whether or not you want to use side exhaust, and the weight.
Some of the non-mainstream brands are seriously heavy. You should get 'em zinc coated as well . ..