The whole idea behind switch rods is that you can "switch" between overhand and spey (single-hand to two-hand) at will. However, there is always a compromise, and most switch rods don't do either type of casting quite as well as a true overhead or spey rod. I've found that if you're going to spend most of the day using it single-handed (overhead) then it's best to put a line on it that casts best that way and accept the slight compromise when using it for speycasting. The same would be true if you plan on mostly speycasting with it with only occasional overhead casts. Then use a line that speycasts best with it. The 6/7 is a terrific size for most Great Lakes steelhead.
I don't know if one can say who the "best" manufacturer of switch rods is. Most of the ones that I've cast (Beulah, Sage, Echo, TFO, Loop, Winston) have all been excellent rods. The same rule applies as it does to all selecting of rods. If possible, try a bunch of them first and then make your decision. If that's not possible, then at least the fact that most of them are fine rods should ease your mind. The biggest problem I've had with switch rods is finding lines that really work well with them. The Winston 11' 7 weight BIIx is a particular bugger that way. With the Beulahs, I stick to the Elixir and Tonic lines that Beulah specifically designed for their rods.
You should also be aware that Beulah is introducing a whole new line of premium switch rods on September 1. They range from a 10'4" 5 weight to an 11' 8 weight. That's five rods total and they have the new lightweight graphite blank that they've use on the Platinum speyrod series and in a whole new series of trout rods that come out this month. If you don't need your new switch rod until this fall's steelhead run, perhaps you might want to wait until these are on the market. Beulah had a couple of prototypes of these at the winter fly shows (Somerset, etc.) and everyone I've talked to who cast one loved it.