I've used a both a dedicated grinder as well as the grinder attachment on my wife's kitchen aid. So far, the kitchen aid has been great for it. Partially frozen is best. What I've done is used a frozen pork loin, take it out and leave it out for an hour or so, or in the fridge overnight. It's best if it's still mostly frozen when you cut it up, but obviously enough to cut it up. The frozen part seems to help with the plugging up part.
The one hint that I learned from the kitchen aid instructions was rather than cutting the meat into 1" chunks, cut the meat into strips. Cut the strips 1/2"- 3/4" wide, but they can be as long as your meat allows. The strip seems to function better than chunks, as the grinder then works to pull the meat through. Chunks seem to require more pushing, particularly wider ones.