WIth divertors, you have to make the choice of whether you want one or the other, or both simultaneously...it takes a different valve to do that which adds to the confusion.
A typical pressure balanced shower valve has no volume control. This may not be an issue since the flow is restricted by the showerhead - the valve can flow much more water than a single shower head can dispense unless you modify it by removing the built-in restrition. Now, if you were going to use the hand-held on say an infant, you might want to restrict the flow. Often, that is only available on a thermostatically controlled valve (but there are a few exceptions). So, for all adults, separate control of the volume may not be a big deal.
As to brands, you need to consider not only style, but construction and availability of parts down the road. Some brands, like Kohler, rarely keep the same thing for very long, and it is very difficult to buy replacement parts. Delta and Moen tend to use the same guts for long periods of time, so parts are often carried virtually everywhere. Personally, I've had good luck with Grohe, but I'm a sample of one. I did need a new cartridge, and they sent me one for free (I probably could have gotten one from the local dealer, but I was in no hurry).
In a big box store, you often buy a 'kit' which includes the valve and trim. In a plumbing supply store, you can usually buy the rough-in valve separate from the trim, so you may have more choices.