It comes down to flexibility, voltage - fixed or variable, connections 510/901/808/801/306, extended battery life & low replacement costs, juice delivery systems - bottom or top juice feeders, atty’s, carto’s , tank mods. The best way is to figure out what is important to you and go from there. A lot of people are very happy with the Ego, some people want more.
If you list what your hoping to achive you will get some good advice.