If you are shooting with the flash off camera go with the Yongnuo 560 IV and the associated flash trigger. Set you back about $110 bucks. If you don't shoot manual off camera it is a great skill to learn and something you can do inside during he colder months. Start with Strobist, lighting 101. Cost you about another $50 for a light stand, umbrellas and clamps. $160 for a full lighting setup that really, really works great.
On camera I would go with the Nissin i60a. TTL but not HSS (yet, they promise a firmware upgrade). Us this on camera all the time. I have both setups and can vouch for both with an XT-2 Can't go wrong with either one. I use both and plan and getting another Yongnuo 560 IV for a 2 light setup.