I know this is personal preference, but for me it is USB C. I have a bunch of USB C style batteries in different sizes and mah's and even the smallest will only be half way down usually less after a typical show. I don't mind the USB C attachment at all, as I have a bunch of decks that use USB mini or micro which is basically the same and I have never given it a second thought. That said my MixPre6 deck is in a portabrace and I recently tried and like using a short USB C male to USB C female cable which stays always attached, so all I do is attach the USB C cable coming from my battery to that. The portabrace keeps the USB C cable firmly in place and there is really no way it can be pulled out with all the velcro and flaps.
For me the kicker is that I am not willing to give up the battery pack as a backup, which while it may not last long, and which I probably will never need, is still there if a battery fails and IMO a backup is always good. I always use an external battery along with with internal batteries on all my decks, even in low pro situations. In all non low pro situations, I keep an extra battery in the bag in case of a failure, although other than 2 of the original tekkeons, I have never had a battery fail during a show. It may be overkill, but it gives me comfort to have 2 power sources.