I'm playing on Agnarr, and I was wondering if I need a higher damage higher delay weapon like, the Stone Bladed Stilletto at 14/28. Or if I should use a lower damage lower delay weapon, Exquisite Velium Spear at 12/20? Any insight would be much appreciated.
You want the best ratio (which is the 12/20 in your examples)... You could swap out the bigger damage for backstabs if you're up for that level of micro-management.
I've never actually done it, you could probably use the bandolier to do it but I seem to recall something about it resetting the delay timer or something... so probably not worth it and more likely to miss other dps stuff worrying about this.