That is a loaded question. I love my pro tank, but I have yet to try Iclear 30s and I hear those are pretty good. There are a ton of choices out there. What I recommend is to take some time and explore. Pick a flavor you know and love and your favorite current device and get just one of a few of the tanks that sound like they might work for you. See how they handle a good test run. It might take you a bit to find one that works, you might end up liking cartos still, but you might just find your new love.
A few general rules to look for that helped me.
If you like warm vape a tank or clearo that has a top feeding atty might be more to your liking such as a Vivi Nova or an IClear. However these types of models you often have to tilt as the tank drains to properly feed the wick.
If you don't care about temp or prefer a cooler vape, something like a BCC or Pro might be worth a test, but I've noticed that if you have a VV you sometimes have to drop the volts at half a tank by one or two points to avoid the burnt juice flavor.
Also if you know the ohms of the cartos you like you might want to see what's comparable in tank attys, and make sure it's offered in the tanks you test out.
Just my thoughts. I hope that helps a bit.