I cannot live without RealGuitar (acoustic) and its electric companions RealStrat and Real LPC.
Once you know how to use them, the strumming is perfectly realistic. (Trick: You should turn Pattern Playing Mode to ON for strumming. That is not clear in the manual.)
If you buy one, I will send you a Sonar starter file that shows how to set things up for strumming. Why? Because I am awesome.
Seriously, I drive everything with acoustic guitars and rely heavily on RealGuitar, although the strumming techniques work for all three products.