Seattle Seaplanes or Kenmore Air in Seattle WA. I worked at Seattle Seaplanes for 3 years, and I know that the Pacific Northwest is the best place to fly floats. I flew for fun at Adventure Seaplanes just outside of Minneapolis, and they are also a really good outfit. I also did some flying with Danny Duggan in TX, but unfortunately the great Mr. Duggan is no longer with us. I've never been to Brown's, but I have heard good things about them.
My suggestion is to go to a place that will take longer than 3-4 hours of flight time for the rating. It may cost a little more, but the experience is incredible when you can actually enjoy it. I had a few students that wanted to do the rating in one day and about 3 hours of flight time.They got their rating, but they really didn't learn anything, and it was all work trying to cover all of the PTS items in the minimum amount of time. Take your time and take it all in, I think it is the most fun you can have in a plane.
Also if you plan on buying your own seaplane, or flying your buddies seaplane, get more instruction than that necessary for the rating. Float flying is great fun, but it can also be extremely challenging, and you can get in over your head without even knowing it. Just think you will now be flying in an uncontrolled and ever changing enviroment of boats, currents, tides, debris, waves, no waves, tree stumps, rocks, and countless other hazards that can make a good day turn bad quickly.
I will warn you, flying floats is extremely addictive.I did my rating at Kenmore Air back in 2000 just for fun, and ended up moving up to the NW from TX and getting a job flying floats. I did that until my wife couldn't stand it(not making much money) anymore.
I moved on to cargo and now a fractional and I really miss flying floats, whever you decide to go, enjoy.