I was in the same boat a few months ago. I really liked what the Pathfinder had to offer, it was in my price range, good off-road capabilities, good family hauler, decent towing capabilies for a mid-sized SUV, had a trucky feel and look. The radiator issue was a turn off and I was looking at the Armada but the brake issue scared me away from that platform.
To answer your question, you're best bet is to find a Pathfinder (as any vehicle really) with a good maintenance history. You'll know right away if the radiator has leaked into the transmission. It will have shifting issues and vibration issues, especially at highway speeds 65+. Some Pathfinders still have the problematic radiator and have not had an issue but most members would agree that they will most likely fail eventually. So when looking at a Pathfinder and there is no history about the radiator or transmission, look at the very top driver side of the radiator and look for the Calsonic sticker with the part number. I believe the known radiators that have the failure issue are 21460-EA215, 21460-EA265 and 21460-EA200. I think there a few other part numbers that are floating around but not 100% certain. You can also look underneath the vehicle and see if there has been a bypass if the radiator has not been replaced. There are two small hoses running into the bottom of the radiator, one on each side. When I bought my Pathfinder, the radiator had been replaced with a Nissan OEM Value radiator and did not have a part number. http://www.thenissanpath.com/viewtopic.php?t=14995
It did not have the bypass so I asked here to see what I should do. I believe this radiator should not have the problem. But only time will tell. Even if you do have a replacement radiator, you could do the bypass if you are really concerned. Most members believe it regulates the transmission temperature since there is already an external trans cooler. So if you live in warmer climate you should be ok to have the bypass. If the radiator has failed, was replaced, and the transmission has been rebuilt by reputable source, then it should all be good.