There are probably more choices in single showerheads verses handheld designs, so it somewhat depends on what you have or have found that you like. To select between two heads, either singly or in tandem means a more complex piping and valve, which over time, you may not find that useful. Plus, if you configure it to be able to use both, you will be taxing your hot water supply and shorten your shower. A handheld can be really nice if the bath/shower is used by both young and old, as the flexibility of sliding it up or down, or taking it off, to direct the spray just where you want it is helpful. But, some would say it clutters up the look.
I think Grohe discontinued it, but there are still some around for sale: Freehander is a dual-head, pivoting assembly where you can shut one of the heads off. They swivel as you raise or lower the loop they are held on - kind of neat, but not inexpensive. Down low, sort of a body spray, up higher, a traditional showerhead (but on a loop rather than an arm).