Well if it's for your own projects that simplifies things a great deal, as you're operating outside of the regular market, and the camera only needs to appeal to you and suit your needs.
If raw HFR is essential, then you're going to have to go with the Red, if things like internal NDs are essential, look to the Arri. They're very similar cameras in a lot of ways - both produce lovely pictures, and both are small boxes that need to be heavily customised and accessorised in order to suit your personal shooting style.
As far as yielding a 'filmic' image, the greater highlight latitude on the Arri definitely gives it an edge there (over both the red and everything else out there). But again, if it's mostly just for your own projects, then you know best what your particular needs are. Personally, I don't think anyone needs to worry about the Alexa Mini becoming 'obsolete' any time soon - it'd be close to being the most popular camera on the market right now (for higher-end work at least).
