I'm currently level 35 speccing Scrapper and it's really fun to set up the fights, tranq a mob, slice the droids and then Backblast an unsuspecting mob. However, it's seems slower than leveling with my Sentinel. My Sentinel (Once I got Doc) I could just jump into the middle of a group of 3-5 enemies, kill them all quickly and not drop below 80% health.
Leveling Scoundrel requires a lot more set up for each fight and ensuring that the odds are in your favor. Sneaking around definitely helps but that doesn't help with the Bonus Kill # of Enemies. Looking forward to 36 for "Shoot First" and then 40 for Flechette Round. Those should help the enemies drop to the ground faster!