The one technical limitation is you can't get Quadra Drive in a V6. If you want Quadra Drive, you need to be looking at the V8 or diesel, it comes standard on the Summit with those engine packages I think. If you tow heavy often, you will probably be happier with a V8 or Diesel.
Otherwise its a subjective thing. There have been several threads here on this subject. A quick search will provide plenty of opinions. Why are you not looking at the diesel?
All engines are adequate and provide plenty of driving pleasure. If its new, off the production line over the last month or two, the initial V6 tranny quirks should be ironed out.
So it comes down to your subjective preference, no one here can address that for you. If you are going to be the type of driver that is always saying I could have had a V8, just buy it and move one. There are much more important things to fret about, I think. Otherwise test drive thoroughly and pick the one you like best.
I'm going to close this thread before it gets to be a peeing contest as there are plenty other comparison threads here.
2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6, 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac