Stainless hardware and frame or just hardware. My experience with the aluminum frames was 2 years ago I grabbed the frame to pull the boat towards the dock and the frame snapped right in half. I had to order another rear bow and it cost me like $50. Salt water you have to have stainless. But freshwater if I have to buy another I'm going with stainless. If you have aluminum be sure not to let passengers touch the frame as support when they get in the boat as they always tend to do because these made in China inexpensive aluminum frames snap like pretzels.
I went with the 48 inch frame size. They can also be cut down with a hacksaw if one gets one too high. I'm 5'11 inches and I can stand in mine while driving. I like the look as low as possible for sleekness. But frame size all depends on how high the boats gunnels are. What size to get is always a popular topic on bimini's this time of year in the forums. The lower the frame the more protection you get from the hot sun.
Tip: get a bottle of
3m High Tech cleaner from Iboats, Walmart etc:
Your sunbrella is going to develop annoying white spots on it. Especially if you put it in the Bimini cover with any moisture on it. Mild soap and a light brushing works to remove it. but this stuff contains no solvents and removes those spots, but also removes grease spots and bird droppings.
I went over my trailerable cover that had grease from touching the O/B control rods and this stuff takes it right off without discoloring the covers Top Gun fabric. It's one of the only cleaners recommended by Sunbrella. They make a protectant too, but you won't need that for a couple of years from now.
http://www.westmarine.com/1/1/10500-303-fabric-cleaner.html