Personally, I felt like I learned a lot from running tons of instances as I levelled. With my all paladin team I did 95% of my leveling in instances, generally only doing quests that were instance quests. It was really, really slow in some cases, but I learned a lot about boxing in instances which helped a lot later on, and also helped me understand some of the more common problems we boxerfolk run into.

The new team I'm leveling is a mix of quests and instances - I'm kind of roaming around zones and doing boxer-friendly quests, and then when I run out of quests I'll run a few instances to pick up the xp slack until I'm able to do the next zone. This has, so far, been MUCH faster and more interesting for me now that I've got the mechanics of boxing pretty well understood and just need to work on my tactics for handling heroics & gimmick heavy encounters.

I'd say you would probably be fine with the second version - mixing quests and instances - because really, running SM 900 times to level isn't going to teach you anything