There are some very strong opinions on the topic of whether to choose a mirrorless camera or a DSLR. Which one is right for you? You really need to put on your body armor if you want to discuss the topic at your local camera club, but here are a few things to consider:
1. A Mirrorless Camera is smaller than a DSLR...
Although true for the body, when a lens is put into place the difference between an consumer to mid range DSLR is typically not much. True, some professional DSLR's are a big on the larger size but on the other hand some of the newer mid-range DSLR's are actually getting smaller.
2. The range of camera lenses are better in a DSLR..
True for quite a while however companies Panasonic and Fuji have a large selection of lenses, with Sony close on their heels.
3. Mirrorless cameras do not have viewfinders..
Early Mirrorless cameras with electronic viewfinders did suffer from distortion and at times pixelation when the camera was moved. Optical viewfinders will always let you see the real world. Of course, technology is improving, especially with the higher end mirrorless camera's with the added advantage of other advanced camera settings without having to shift your view.
DSLRs obviously have the capability to take stills and video with amazing good quality that rivals some of the dedicated video cameras. Mirrorless cameras are catching up though with 4K capability (Panasonic GH4) that many people find desirable as the next step in video production.
5. Image Quality
In order to design a smaller body, the image sensor must be smaller in a mirrorless camera. Some commercial, sports, and advertising photographers need the highest image possible. Some of these images may actually be placed on billboards. If you are taking vacations photo's and posting them to social media or printing 8x10's a mirrorless camera may produce some excellent images.
DSLRs can generally still out perform mirrorless cameras, especially with fast moving objects such as sports photography or wildlife. The exception in many except some of the high end DSLR camera is in the case of live view. Phase detection switches to contrast focusing which slower and may not be as accurate with live view. The lenses in mirrorless cameras are designed around the sensor so focusing can be a little faster and more accurate than with DSLR's in the live view mode.
7. Frame speed
The top DSLR has a frame speed of 14 frames per second, whereas a higher end mirrorless camera can have a frame speed of 60 frames per second. Do you shoot action? Keep in mind the Focus topic above.
8. Battery Life?
Are you outdoors most of the day shooting without an electrical outlet nearby? If so, DSLR's remain a good choice for you with almost all mirrorless cameras having a shorter battery life than most DSLR cameras.
In the end, you have to ask yourself what type of photography are you interested in shooting. DSLR's are still preferred by many professionals for some of the reasons listed above. Mirrorless cameras are quickly closing the gap and more electronics mean less moving parts and possibly less down time.