Personally, I like the Professional's Choice brand. I have used the SMB II in the past but I recently bought a new pair of their SMB III and I just LOVE them. They fit even better than the SMB II's did.
Yes, the SMB III are expensive but they are high-quality boots that are going to last you a long time if you take care of them. The SMB II boots that I have are at least 7 years old and they are still in perfect working condition because I have taken care of them and cleaned them when needed.
So think of the boots as an investment toward the safety of your horse. I definitely recommend getting the SMB III sport boots on all four legs, along with bell boots for the front legs to protect against over-reaching. I prefer a bell boot made with the ballistic material because it is really tough and won't wear down as easily or quickly as a neoprene bell boot will.
This is our get-up with our Professional's Choice SMB III boots on all four feet, and Classic Equine ballistic bell boots on the front feet (that we won at a horse show for 5th high-point adult).
My mothers horse (the dark one) is standing on the right side of us and she has Professional's Choice SMB combo boots on the front legs and those 7-year-old SMB II boots on the hind feet. As you can see, the bell boot portion on the combo boot has had repairs (which is why I don't like the neoprene because it can be ripped off), but they still do their job and protect her legs.