As always, decide on the mission first.
As others have said, if mostly flying by oneself, the -8 is the best choice. If often flying with a passenger, the -7 (actually, the -14) is better suited. A tandem aircraft is a pilot's airplane, first and last. It'll make passengers feel uninvolved with the flight and the pilot. A side-by-side arrangement is just the opposite; it's ideal for sharing the experience.
I loved my -8, but my wife never did. Although, from the pilot's perspective, there's no substitute for centerline seating, I'm building a -14A now in the hope that she'll feel more involved and less like ballast.