I have had my Jeep for a while now (V-
and I would pick it over the I6 - I would say the I6 is possibly more bulletproof (as was the one in the ZJ) but uses very similar amounts of gas
I have replaced my radiator, water pump and now catalytic converters, the engine still runs like it came out of the whow room in the year 2000 - quick, responsive...I have 140,000km now and am confident I have another 140,000kms.
Like others have said, find one that has been looked after ( at least oil serviced) and you should have minimal issues (apart from wear and tear)
Go for the V8.