Its got to be the DR400, so much nicer to fly, faster, roomier, better viz, easier to get in and out, better strip aircraft.
The only disadvantage I can really see is if you want to keep the aircraft outside. A DR400 really needs a hangar. Ive flown DR400s a lot and various models of PA-28 quite a bit less, but the DR400 wins hands down. Cant say about spares and maintenance as I only flew Club aircraft. As it was in France, there never seemed to be a problem with spare parts. Another interesting comparison was a trip to the PFA rally up from Toulouse. I was in a DR400 160hp fixed pitch prop, my friends in a TB-10 180hp, constant speed prop. Both aircraft two up. The DR400 got off the ground quicker, cruised faster and landed shorter!