I can't say much about Minimed, but I can say that I love my Dexcom. I do wish, however, that I didn't have to carry a separate receiver for it... If I already had a Minimed pump and planned to stick with that brand, I think I'd trial the Minimed CGM. Even if your current pump can't automatically pair with it, your next upgrade should. (In fact, I trialed Dexcom because I have an Animas Ping, and Animas and Dexcom will be integrated.)
The most common complaint I hear about Dexcom, by the way, is that the alarm isn't loud enough. I don't that problem, but it seems a lot of people do. I have mine on "vibrate then beep" most of the time anyway, and will usually notice the vibration easily... even when I'm asleep and it's just against me.
The insertion isn't bad at all. I was intimidated by the inserter, but it's not as complicated as it looks. I also don't think it hurts any more than inserting an infusion set. Well maybe, on average, a tiny bit more of a "pinch." Everything seems to stay in place pretty well, though I sometimes dab a little Skin Tac on an edge a day or two before the sensor change is due.
Oh, and the accessories suck! :p The receiver comes with a rubbery skin (mine is gray) and a really ugly black canvas and clear plastic belt-clip case. There doesn't seem to be any Dexcom accessories for sale anymore either, so expect to buy a cell phone case for it if you want to wear this thing on your waist... a small price to pay for technology I like, though.