Some say that I4 guys are really just 8 cylinder guys who know that an I6 isn't going to match a good "V8" -- so they just buy the I4. The first, WW2- era Jeeps came with I4s and when I think of a "Jeep," I kind of think of those. The I4s in those vehicles did the job vs. vehicles from the Land of BMWs and Mercedes. I4 is not a Honda-type engine...it actually has decent low-end torque and a none of the sound characteristics of front-wheel drive vehciles you might be familar with.
I6 is a solid engine with good torque (speaking for 91-95 YJs and all TJs). Mileage, however, seems like it has always been a mofo with it, though. A few years ago, that might not have been a big deal. I get 20mpg with my I4 on the highway (and cruise at 80mph; 400 mile range on my 20 gallon tank)...I6 is lucky to get 15mpg, and often-times more like 12mpg highway (don't buy the "18mpg" on the window sticker BS...ask around).
Both I4 and I6 are well-proven, though. And, both will take you where you want to go when you're in low-range. I dig the I4, as do most of the people here. But, your friends have a good factory engine with the I6.
The I4 ain't for everybody.
