I like both. Mirrorless has a big future. Once the AF gets up to speed and the EVF evolves sufficiently, what else has to happen? Based on the game-changing specs & performance & gob-smacked reviews of the mirrorless Panasonic GH-4 I bought one for my video work where it tidily beats the pants off my 5D3 in all situations with the exception of high iso shooting (over 1600 iso).
After using the GH-4 for a couple of months I'm discovering the sheer brilliance of it's very decent EVF and surprisingly good AF; much much quicker and accurate than I initially expected. Now that Adobe DNG converter v8.6 and Lightroom v5.6 can see the GH-4 RAW files, I've even been using it for stills on some commercial jobs.
Mirrorless is evolving fast. It's great to use. I'd hate to see favourite mainstream manufacturers (cough, cough..) being caught flat footed as this revolution gains pace.
GH4 is a brilliant tool for video. Have you tried the Sigma 18-35/1.8 via SpeedBooster on it? Some say it helps to overcome the high ISO disadvantage very effectively.