I have never heard of any problems with any HK pistols. I have an HK 9mm and have never had any problems. My buddy has an HK USP 45 that he's had for years, hardly ever cleans/lubes it and has never had a problem. He cleans it MAYBE once a year, while still putting more than 2000 rounds through it a year. IMO go with which ever one has the best grip for you. If you don't have a good grip, it doesn't matter what type of pistol you have.
I was also down to the HK45 (not USP) and the FNP45. Both felt very nice in my hand. This was my first handgun purchase so a lot of homework went into my decision (took me 2+ looong weeks to decide). I decided that the FNP45 had a "feel" that I liked and although price was not a major concern, I felt the FN offered more bang for the buck. I've put about 800 rounds through my newish FNP45 and couldn't be happier. Not a bad load in the bunch. Again, this was MY decision, you could have a completely different opinion and that's cool. Just my .02
PS...Having said that, my friend is looking at .45's now (his wife pretty much confiscated his S&W Sigma .40) and he may buy my FN and I will try the HK45. We pretty much shoot together, so swapping/comparing pistols might be fun. That would be a couple of months down the road, although he better hurry, I may not want to sell the FN. I love it!! My advice is shoot both if possible, at least carry the guns around the store for a while to get a feeling for the grip. Last but not least and again I have not shot the HK, but the recoil on the FNP45 is almost non existent. No more recoil, maybe less than the S&W .40 if that is important to you. I'm 6'3", 285 so my observations may be different than yours. Good luck and take your time.
The HK45 is an excellent gun. Haven't fired one yet, but if it's anything like the P30 I shoot regularly it's a winner. The grip is second to none on the P30 and the HK 45. I will probably end up with one eventually.
The USP has always been a great gun. Accurate and reliable, mine have never had a single malfunction of any kind in some 1000 rounds each. The design of the USP absorbs recoil very well.
The FNP-45 is alot of gun for the money. I bought the FNP-45 before I buy the HK45 mainly because of capacity. The FNP-45 holds 14 rounds versus the HK45 which is only 10 rounds. That and three mags instead of only two and along with the price pushed me in the direction of the FNP-45. Also, I've already got my fair share of HK's to play with and wanted something different. :?