Am I correct in assuming that the most well proven and rugged 9mm HK handgun is the USP?
I would say there's little to no difference between them in terms of ruggedness or being "proven," as they are all direct descendants of one another, down to nearly identical internals.
The USP has been around the longest, followed by the P2000 (different grip shape, replaceable backstrap, ambidextrous slide release), then the P30 (most ergonomic grip shape, replaceable side panels along with the replaceable backstrap, decocker on the DA/SA version moved to the rear of the slide, ambi slide release, different slide "styling"/front slide serrations, larger magazine release tabs).
The P2000 and P30 "inherited" the USP's "proven" design. FWIW, the P30 was the subject of a test that ended at 90,000 rounds.
I must admit I a bit confused by the P2000 and P30, trying to place them on a scale of pro/con.
There's no real "technical" reason to rate one above another, so the choice is personal preference -- you really have to put them in hand and see which one "speaks" to you. To me, the only significant difference beyond the feel of the grip is the P30's movement of the decocker to the rear of the slide -- which is not an issue if you start with an LEM trigger version. As to the rest of the controls even as a left-hander, I'm so used to operating right-hander USPs and 1911s with my left hand that the addition of an ambi slide release on the P2000 and P30 wasn't a reason to prefer one over the other.
Disclosure: I have .45 USPs, and P30/P30SKs in 9MM. This is not a caliber-based preference between the models, it reflects the availability of different models at the time of acquisition over the last 20 years, and the specific use cases. For example, in 1999, the USP was the only choice and at the time I was shooting mostly .45. Flash forward to this year, and I have a USP Elite .45 because they became available in a short production run. If a 9MM USP came along at the right price, I'd grab it, but when I decided to go 9MM I chose the P30L for the ergonomics, and yesterday picked up a P30SK for on-body CCW (actually, our 2nd SK, as my spouse decided the first SK was hers!).