Personally I came to notice that both games are great, for me personally though I do not like seasonal games that much, having to do the same thing over and over again is not my thing however I like the gameplay, specifically in path of exile there is a LOT of depth while in diablo 3 the game feels smoother and the repetitiveness can be excused since you are not kinda forced to replay the whole campaign. It is a turn off for me to replay the story of path of exile while the game itself feels superior in many ways such as build diversity and combat gameplay. Path of Exile is very fair for being free to play, one of the best in the market however the ability it gives you to buy tabs with real money is a turn off because lets face it... you will need those tabs to store your items since this game is a looter.
Overall both games are great.