Personally, my set up are 510 mega cartos from Nhaler, blank, soft tips for open and drip fill.
However, this set up works better on a 5-6v device since the resistance on them is higher so they're more in-line with higher volt vaping.
If you're rocking the 3.7v options then obviously the first thing you're going to want is to find one with a lower resistance so you don't immediately turn yourself off of cartos since the ones I use suck horribly at 3.7v with little draw, taste, and overall feel since it's just not getting it hot enough.
If you're an LR lover, there are LR cartomizers, I believe Bombdropsvapor has them, amongst other vendors. It might take some trial and error unfortunately, but everyone has a different perfect scenario.
If you haven't tried low res, and like the performance of normal resistance ranges, go with a 2.0-2.8 (max) resistance cartomizer. Anything in the 3 range and you're going to have severely decreased performance.
Off the top of my head, I'm completely unhelpful regarding vendors that have them in this specific range so maybe others can chime in on that as far as 510's go.