Interesting. Based on these screenshots:
Luigi's Mansion 2 > Luigi's Mansion 1
Super Mario Sunshine > Super Mario 3D Land
Mario Kart: Double Dash > Mario Kart 7
Mario Party 3DS > Mario Party 4
Paper Mario 3DS > Paper Mario GC
Mario Tennis GC > Mario Tennis 3DS
Revelations > Resi 4
I'm undecided on the Pokemons. That screenshot of Colesseum or XD is hideous; but X/Y aren't really lookers either. I'm undecided about the Smash games too. Objectively I think the 3DS version looks better, but the black lines around all the characters is really offputting.