I also vote for the Boge LR and the Duallie.
The Duallies have a few quality control issues and I've had a few not work soo well, but when they work, "Woah Baby" they work well.
The Boge's have been around for a long time, however, and are more consistent. Vapor and flavor are as good, (well vapor is a slight bit less).
I will say, however, I've been using the Bloog LR on a KR808D-1. That has been the best as far as flavor goes..
......
The question was asked about how many times to refill. I think much depends on the juice used and how soon it clogs up the carto's. I've had a few cheap carto's I've refilled as many as 18 times, but must admit, the flavor and vapor dropped off drastic. I've also had a dark chocolate flavor that will kill a carto in 1 to 2 fills. The 808 carto's can be boiled and reused (with some successes ), and I've heard the 510's cannot (dunno).
I use a cig size exclusively and have for a year now. No desire to change up. I LOVE cig size.
And I use the KISS method (Keep It Simple, Stupid!)
Pig