Rift Mage is very tactical and focuses on control and support but can still pack a punch, if you like pausing the game and making sure nobody takes unescessary damage, setting up combos and generally controlling the battlefield, Rift Mage is for you.
KE on the other hand is very versetile but becomes immortal if you pick the Fade Shield passive, that one little passive just breaks the game if you enjoy risk and challange. Hower if you don't pick it, it's a very fun skirmisher than can deal some heavy aoe damage, since you aren't immortal you can't just stand there and spam spirit blade and need to think about what's going on around you and what your doing.
I like to use Static Cage(upgraded it's a big dps boost for your entire party ontop of beeing decent CC) and put a Fire Mine in the middle, when enemies get draged into it and stunned i rush in with Iron Bull and detonate the paralyze with Whirlwind and with the enemies attention focuse elsewhere i can help aoe in melee with Spirit Blade and Immolate.
If you do get some attention or your barrier is on cooldown you always have Face Cloak and Fade Step to fall back on, the former also beeing pretty nice offensively aswell.
You can ofcourse do all that with Fade Shield and be immortal while doing it, but man is it dull without any sort of risk.
On the other hand, if you LIKE beeing obscenely OP you can pick Fadeshield and Chaotic Focus(from the fire tree) you can run around doing massive damage with fire spellls while beeing immortal. Chatoic Focus drains your barrier to boost your damage with fire spells, but since you get barrier from doing damage you just end up getting it all back instantly. WIth this setup skills like Fire Mine will start doing alot of damage, the biggest crit i got from mine on an undead(weak to fire) was somewhere around 13k.
tl;dr - Rift Mage: Tactics KE: Versetile and really OP unless you don't take broken passives but very fun without them.