Hi, well, I started with photography about a year ago and had the same issue with which camera to choose, and I went for a basic dslr, a d3000 to be more precise, and don't regret that, even being so basic gave me most of the functions I wanted plus not that much weight to carry, and helped a lot to learn more about photography and how to use it. Also thought about mirrorless, but the choices here in my country weren't that plenty at the time. Right now (because of a lucky warranty issue) I have a t2i which is a bit more rich in features than the d3000 (plus video) and am really happy also, but went and bought a mirrorless also, but have to say doesn't feel the same, quality is good but not as good as my dslr.
I think it all comes down to what you want to do, how much you want to learn, how much weight you want to carry and the size you want to manage. Mirrorless have good options for lenses, but not as many as with dslrs, sure you can go with an adaptor for the mirrorless, but most of the times you'll have to deal with manual focus. Also is not the same feeling on the hand, the grip most of the times is different, unless you go with a beefier mirrorless, and still not the same. I think both cameras are around the same price point, so price difference is not the issue here.
If you have a chance to check them physically on the store do it, a simple thing like the size and the way it feels in your hand is really important, who knew, I prefer using my dslr to my mirrorless just becase of the feeling on my hand, the mirrorless takes great pictures, really great pictures, but as I told you the feeling is different.
The d3100 is a great camera, really cheap and there's practically nothing you can't do with it, lacks auto bracketing and 30fps video on 1080, but the outcome is going to be really good.
You should make a list of the things you want to accomplish with your photography, what kind of photography you want to do, how versatile you want your camera to be, and features you would like to have in your camera, that plus the feeling in the hand, viewfinder, screen resolution, etc. After that check the specs of each camera and see which one on paper is more for you, and also see them at the store, test them, and see which one suits you the best.
Maybe along the way you run into another model at a good price and end up with neither of the first two.
good luck with your first non point and shoot camera.