I started out with a Cue pod that has pre-filled cartridges then looked on the internet and found a few 'stoners' had figured out how to refill it with your favorite sauce.
Soon after I tried a JoyeTech Penguin since it is refillable with about 9ml of liquid and has a selection of drop in choices. 0.25, 0.6 and 1.2 ohm in a ceramic cartridge with a nice wick.
Not long after that I tried the JoyeTech Dolphin. The tank is refillable without removing the drop in and it has a tighter draw than the Penguin, yet produces more vapor than the Penguin but....
If you want tastey, fruity stuff these will leave you wanting. And if you are a cloud chaser using anything thicker than a 60/40 vg/pg and you chain vape the wick won't keep up well. I've found they all work fine on 70/30 but you have to clean the wick from time to time to avoid dry hits.
50/50 works great. Also great at producing satisfying tobacco flavored vaping.
I'm an MTL'r and like the drag from the Dolphin more for tastey flavors. I like the more airey drag from the dolphin for tobacco flavored stuff. It's just more like an ultralight cigarette than the Dolphin. The 50/50 in a Dolphin makes me cough where in the Penguin all that extra airflow causes it to be a smoother drag. I use 0.6 in both. 1.2 wasn't enough flavor and the 0.25 was just too 'hot' for me.
I tried the Air and Drop for one day and gave them away. Yet both are pretty close to the tobacco stick in the way they behave. Both are good at their role, but salt nic caused me to feel asthsmatic in just a few puffs. Perhaps a non salt 12-18 nic would have worked for my use.
Oh, and I've charged the Penguin about once a week and the 8ml tank full lasted through like 4 charges.... it's a sipper.