I hate Path of Exile's skill tree. I don't theory-craft and it's a mess unless you spend hours reading all the descriptions. I just want to play.
Grim Dawn is the ugliest of the three mentioned. It looks cheap but is a ton of fun to play. I also don't like their inventory system.
Diablo III seems the most fun of these games but I'm not a huge fan of most of the builds.
I've played them all multiple times along with Titan Quest too. Titan Quest has the most interesting theme. I'm not a huge fan of their socketing system. Finding 3+ of every item before you can get full use of it is kinda goofy and GD followed that same idiocy.
Please crpgnut, do yourself a favor and stop playing aRPGs