I have an iStick with a nautilus tank. If you're having issues with getting a good vape though the best thing you could do is not use cheap replica tanks. I'd recommend the iStick because you have more control over how much power you're using, which is good when getting the flavour right if you use a variety of liquids. But a better tank allows you to adjust airflow. Atomisers in the nautilus produce a better vapour than evod atomisers too in my experience.
I would always upgrade tank first, if you've got standard ego batteries try one of the Aspire tanks which use their widely available standard 'BVC' coils, I like the little Aspire K1 glass tank, it's like a baby Nautilis! Then maybe an iStick, the 30w is ample. Then you can try a mini Nautilus. That's how I would do it.
Agree with Polter, a tank upgrade would be a far better first step. Personally I love my Nautilus mini and would go straight for that, I think it's the best mouth-to-lung option. Also agree that a 30w istick is ample power if you don't want to sub ohm; the coolfire IV 40w is also a good option.