In theory mineral oil is better because it lubricates better…I think I also heard that it absorbs water less.
Maybe true, but DOT fluid does not “disappear” magically like shimano brake fluid.
Plus druid I use both formula and hope without any problems can’t say the same about shimano, but it’s not like you’ll ever going to get close to the boiling point of a brake anyway 😉
To be honest, the only persons who use shimano brakes around here are the ones whos bike was fitted with them. Formula is the favourite choice. Then comes hope. Then avid and shimano are both hopeless. At the trans provence, no formula ever required a bleeding. I can’t say the same about the avids…