I own no HKs, though "Collateral" has me thinking about picking up a USP some year soon...
For full autos, the MP5SD is absolutely my FAVORITE non-belt fed full auto to shoot. I wish the danged things weren't $12K or more for us enthusiasts. We had a "let the secretaries shoot" day at the range, and the SD was the FA we introduced them to (they were all too scared to shoot M4s or M16s, even the ones that had significant firearms experience. heck, I can't even get my WIFE to shoot my M4). They all loved it. It is gentle and easy to shoot.
I caught the link to those POF-license built MP5s the other day. We need at least one (I have an MP-5 sims conversion kit and no MP-5 for it) and $800 seems pretty darned cheap). I also hear that HK sells used and refurbed MP5s to LE agencies. I may need to pick up a couple for the Armory, although we have replaced 9mm subguns in active service with M4s and variants thereof (it doesn't cost much to turn a $20 surplus M16A1 into a nice little CQB carbine compared to buying a new one).