I started with V4L last October and I'm still using V4L - no other models. I guess I'm just lazy.
I was not a fan of many of their original and premium e-juice flavors but I love the Wow cartos and juices; they are very good. I love the batteries, my pass-thru, the good customer service and pretty much everything about V4L. Having said that, I have had a few bad batteries and cartos along the way. All were replaced without question.
Most smokers just want an e-cig model that gets them off the cigarettes and provides a smoking-like experience that is an acceptable substitute. For some people, that's the 510 because they like a cooler vape with more vapor. For others, like me, they want a warm flavorful vape with a great throat hit. Still others want a very hot vape with tons of vapor but at the expense of flavor.
This is not rocket science: just as there are many different types of tobacco cigarettes in terms of how they taste and feel, it's the same with e-cigs. I was brand-loyal for years and couldn't stand cigarettes that were too strong (like a mod) or too weak (like a 510). I couldn't smoke menthols.
For me, the KR808D-1 is my new brand, with the added bonus of being able to try different flavors. I love my e-cig. It works, it's very tasty, and I no longer smoke. That should be the criteria used to evaluate any particular model of ecig: does it work? Does it make people happy? It seems obvious from the postings I've read on this forum for nearly a year that the KR808D-1 is one of the top performers, along with the 510 and the new Ego/Riva models. I don't think enough vapers use mods yet, so they aren't even in the top five.