I really like the grip and trigger on the USP over the P30. The USP has a more standard grip that is easier to conform to because it is similar to most other guns out there. I find the USP to be easier to bounce into and just pick up and shoot. I also shoot the USP very accurately but the shot recovery time can be aggravating. The P30 deffinitely has some features I really like. I think it has one of the better slide designs I have encountered in a duty style DA/SA. Conceals well, the slide serrations and slide shape are very agreeable to me. I also think it is probably one the most flat shooting, light weight, plastic DA/SA guns out there. I do not like the P30 grip, and I think the VP9 feels a little worse. The large dished out beavertail area prevents a good grip unless I run a smaller backstrap which makes it fairly small for a good two hand grip. The trigger guard on the P30 is silly.
I am of the thought that the shooter needs to conform to the pistol as a general rule (some people and some guns will never mix well). I think if I gave the P30 a year of work I would probably end up preferring it to the USP but the HKs tend to not be my primary shooters so I don't know if that will ever happen.