Our club has a pair of 172s and a 182P (with the Q engine). I LOVE the 182. A big, stable, comfortable cross country machine. With the upgraded panel (Garmin 650, etc.) it's really nice. Think - 172 on steriods. As noted a while back, take the 172 numbers, add 5 knots and you're in the ballpark. Oh, and remember, trim is your friend. You may get sloppy with a 172, but you MUST trim a 182. Save your firewall, it can.
Now, for payload - our 172N with the Penn Yan 180 hp conversion is the winner. With full long range tanks I can put 755 pounds in the cabin. The 182, with full long range tanks, can only take around 650 pounds. Yes, I know about leaving fuel in the truck, but the club rules require putting a plane away with full tanks, so all my planning has to be with that consideration. However, it is typically just my wife and me, along with minimal baggage, so it isn't really important.
If I were to buy only one, I'd get the 182. Did I mention that I LOVE that plane?