Liberty: MY aunt and lead guitar player in my band have one. They're chick Jeeps and I will never forgive them for replacing my beloved XJ and swapping the 4.0 I6 for the 3.7. That being said they seem very reliable. My aunt is a terror on vehicles. Once drove a Neon 80,000 without a single oil change. Her's is still truckin'.
Explorer: Not too bad. Have had many friend/fam have good success with theres but some not so good. The upside is they're easy to work on with parts readily available. Same with Jeep and Chevy.
Grand Cherokee: I can't express to you enough how much I love these things. I still prefer the 4.0 I6 over any other engine Jeep has used but I'm biased. I beat on my XJ and my brother beats on his ZJ but those 4.0 engines just hold on tight and keep going.
If you can't tell I love and 100% recommend Jeeps. I haven't personally owned an Explorer or Blazer so I won't get into a pissing match about which is better. Fam/friends have owned both but I've seen mixed results. I personally have never seen anyone get a Jeep and be dissatisfied. My buddy, the guitar player, really didn't want a Liberty but got a KILLEr deal from his Father In Law and couldn't pass it up. He now loves it and says he may be a "Jeep guy" the rest of his life.
I'll tell you one thing, once I can get out from under my 2 current VW's I'll be going back to Jeep. I'd rather drive a rusty 88 Wagoneer than deal with these things.