How Does Sonar's Strum Acoustic Compare to MusicLab RealGuitar 3?

I have both and use both heavily, but I use RG a lot more..  The NI product does sound fantastic but it will only play the preset strumming patterns built into it, and will only play the chords it knows.  The second issue (finite number of chords) will only come up if you want exotic or chords.  You may find the inability to create your own strumming patterns limiting, however.  What it does, though, sounds awesome and the ability to adjust voicings is great.
 
RealGuitar will allow you to play BOTH the chords it knows (chord mode) or custom chords (keyboard mode) and since strumming is controlled by keyswitches, you can do any strumming pattern imaginable.  It will also do solo guitar parts, finger picking, and it offers steel, nylon, and 12-string guitars.
 
If you don't need anything fancy, NI is a great deal and sounds good enough for any record.  If you depend on acoustic guitar to drive every song (which I do) and you use complex chords or custom strumming, you probably need RealGuitar.  Example: NI does not have a good straight 8ths pattern.
 
The RealGuitar manual is not super easy to understand but I can help you, and so can several others on this forum. It is very easy to use once you get a couple of ideas down (like pattern playing mode).
 
PS I also use RealStart and RealLPC from MusicLab, but RealGuitar is my backbone.

I think Orange Tree's strum engine is the best, simple and intuative and very effective. Steel Strings and Strawberry will now work with the free Kontakt player and also support NI Komplete Kontrol standard so they are options for those who do not have the full version of Kontakt.
 
You draw the strums on a graphic fretboard and assign an articulation. So its pretty easty to have a upstroke palm mute on the top four strings alternating with a half palm mute down stroke on the the bottom 4 with a 6 string sustain to finish the bar, if you get my drift.
 
Of course you can also drive the instruments with MIDI. the various articulations are velocity switched. Its simple to set up velocity switching using a sliders on the interface.