Sawbones Leveling
- Easy leveling since you have Corso
- Quick to find groups/ easy to kill Elites for the bonus missions when going solo
- @20 you get SRM and Tranq Shot for cc which smooths out leveling even more
- Fun in PvP towards the last half of leveling i.e. 25 and beyond, before that it can be frustrating
Scrapper Leveling
- Decent dps for burning down mobs
- Doesn't really pick up till 20, 25, 36, 40 (these levels are the spec milestones)
- Can be "fun" in PvP while leveling, but I won't lie you will get frustrated with the amount of work you have to put in to kill an Imp
All in all try both out and find what appeals and is most fun for YOU. Everyone may have a differing opinion, but you're paying to play by your own measure of what "fun" is.