Whichever meat you can get, really. I use a lot of rabbit, as it's the cheapest meat I can find (£3.50 or so for a kilo) but chicken is great, and beef, and lamb if the cats like it - mine hates lamb
I feed pork too, but I know some people advise against it because of a disease that can be in pork meat.
I'm sure they'll be fine with the mince, it's just a bit more risky than regular meat
I give mine mince too, when I have some spare from my own dinner, but I wouldn't go out and specifically buy it for them.
I found this raw feeding thing to be quite scary when I first started reading about it, but it's quite simple really. Just think of what a prey would contain, and then try to replicate it. So, mostly just meat, and then a little bone and a little liver or other organ meat. That's it really! Then give some raw fish once a week and you're all set.