The tanks I'm talking about are carto tanks, mostly the DCTanks. I cut the tank tube down so a regular sized Boge carto will fit. I use 3.0 cartos on a VV mod, but on an ego or epower, you'd want to use lr cartos in the tank. It might be a little top heavy on your pv's, but you can see the juice level. Obviously, I love my tanks. There are other tanks options, but I do not use anything else, so I really can't comment from experience.
I mainly use only DCTs just due to their price. If I lose one I'm not out that much. I usually don't use dual coil cartos though. I typically use 3 ohm single coil DCT replacement cartos.