Hmm, well I'd be biased to say 3rd Gen cuz that's what I got. For your intended purpose either would be satisfactory. From what I read, the 4G w/have a better ride, not sure how much though. For certain the 4G w/have significantly more pep, acceleration due to the 4L (w/VVT) engine vs 3.4 (w/No VVT), mileage w/b close to the same.
Front/backseat space appears about the same to me but I've noticed the rear compartment is quite a bit Smaller (shorter) on the 4G, not sure how that happened but I measured about 9" shorter inside, that could Really impact all you want to carry back there, so check 'em both out carefully on this aspect.
So I think it comes down to Looks, which do you like better? Or maybe power, do you want more pep? Perhaps you should drive each to get that feeling for yourself.
Then you have to consider how each appears to have been maintained. I always head for the hood, check out the air cleaner (dirty/nasty?) and check the trans/engine oil to see their condition.
You still have some time, I would keep my eyes peeled, there maybe other good ones just coming up. Don't forget ebay-great finds there too.
Luck, let us know what you do.
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2001 Limited 4WD - 346+K - SunfireRed\Thunder Cloud; - 265/75/16 Michelin A/T2s - Fat Pat's 1.5" BL - StopTech ANGLED rotors - In series 699 trans cooler, New Yota1 transmission, All new OEM suspension front to rear.