I've been using an ego. My next one will be a Buzz Pro.
IMO, once you get something past the eGo, it should be variable voltage. (VV) I've picked out the Buzz Pro, but the same folks make the Infinity Pro, and there are other popular ones, like the Provari and the Darwin.
In the sub-forums where the Buzz Pro folks hang out, there is a poll about what voltage people liked best - their sweet spot. Over 75% of the votes were in the 4.0 to 4.75 range. The only way you have any options in that range is to use a VV system. And using a VV mod, you can dial in to what you want, and you can easily adjust if you want. Some flavors, for instance, do better at one voltage, where another juice might make you happier with a little higher or lower voltage. With a VV system, you can always get what you want.
I can't understand paying a lot of money for any mod that doesn't do VV.