That's a tough question to answer.
Mirrorless is the wave of the future, and the big brands (Canon and Nikon) are moving aggressively into the market. In doing so, they are quickly dropping their DSLR lines of cameras and accessories, which are becoming harder and harder to find new. Other brands, like Sony and Fuji, switched to mirrorless some time ago.
If you want to keep on top of the new technology, and ensure that you will be able to purchase lenses and other accessories in the future, than mirrorless may be best. Unfortunately, at the moment, there are limited offerings from some manufacturers, and many of them are quite pricey. It will take a while for the companies to build their product lines and fully cover both the consumer and professional markets.
DSLRs are still a good choice of camera. The problem is that some manufacturers have stopped making not only the cameras but also lenses and other accessories. While it's still possible to find some of them new, most of the products are quickly becoming unavailable as existing stocks run out. However, if you have access to a DSLR and accessories, there's no reason why you can't stick with it for the time being. And, as more people make the move to mirrorless, a lot of DSLR lenses and accessories will find their way into the used market. Finally, there are adapters available that allow you to use DSLR lenses on the newer mirrorless cameras, so you can continue to use your existing lenses even if you switch to mirrorless down the road.