To be honest, after having experience with both I would just recommend getting the Mark 2. The only reason for this would be because the autofocus tracking (when I do wildlife photography) is definitely an improvemen over the Mark 1 when I'm using 9-AF zone tracking on AF-C. Also, as has been shown by the official PF review, theres no stareater with the built-in RAW noise reduction, though I must agree it does sometimes make me nervous that some software might create strange artefacts at some point. This is just an irrational worry of mine since my thinking about RAW is that it should remain untampered with until the photographer decides to tamper but that's just me :P
In reality I've had no issues on Capture One 20, Lightroom 5 or CC, Darktable or Affinity Photo (which is what I use mostly nowadays). That's my expereince on a Macbook and an iPad. In fact, the noise level at 12,800 is ridiculously low when you're careful with noise reduction, sharpening and sharpen-masking sliders in Lightroom. Not had to use flash at all walking around London in darkness (as dark as it can get in an overwhelmingly artifically-lit city at least).
However, from some actual side-by-side testing I've done, the Mark 1 does outperform the Mark 2 by about 60 shots on battery life. Also the Mark 1 seems to last a good hour longer in Live View mode than the Mark 2. Then again I just carry 4 batteries everywhere I go and don't really think about it. Plus theres always the battery grip if you're gonna use it for extremely long exposures or video.
Hope that helped more than confused.
David