We actually wrote a whole article on this very subject which you can find here. For the purposes of this FAQ page we're going to feed you the short version.
Below you will find our summaries of each of these two brake fluids. Let's begin with DOT fluid:
As you can see, there are a lot of positive points about DOT brake fluid, not least the fact that it can be found pretty much anywhere at less than half the price of Mineral Oil. There's good news and bad news when it comes to it's water-absorbing properties, that is why you'll find I have entered it in both tables to show both sides of the story.
On this particular point I personally feel that the benefits massively outweigh the drawbacks. Changing your brake fluid annually or bi-annually (depending on your needs) to conquer the drop in boiling point is a small price to pay to avoid having water pooling in your brake system.
Also the fact that it is regulated by the federal government means that the brake manufacturers can concentrate on building brakes instead of formulating brake fluid, and be safe in the knowledge that the DOT fluid they're designed to be used with is of consistent high quality regardless of who should manufacture it.
A huge disadvantage of Mineral Oil, or proprietary brake fluid, is the cost. As it is one-of-a-kind, there's no competition (as such) and the warranty says you should use it, they can basically charge what they like for it - and they do. Not cool!
In contrast to DOT brake fluid, Mineral Oil is not a regulated fluid. This means that the likes of Shimano and Magura have the added freedom when it comes to it's manufacture. Shimano certainly see this as an advantage as they 'don't have to trust anyone else's testing standards' and can pretty much guarantee the results. A sceptic would also point out that they can also make money off the back of fluid sales as an extra revenue stream.
Another great thing about Mineral Oil is that it does not destroy your paintwork, something which is very important as bikes and bike gear gets shinier by the week. Don't blemish that bling now! :)