Unless there in something wrong with your SIG, I am surprised at the bad DA trigger comment. For DA/SA pistols SIGs have about the best DA trigger of any handgun I have handled. HKs DA triggers have improved greatly over the past few years. My most recent HK is a USP45f. It is AD datecoded as 2003 mfg. The DA trigger on this thing makes my two other AC datecoded USPs seem like crap, and they are not bad. However, as good as I think the new USP DA trigger is, if you aren't doing well with a correctly functioning SIG you won't do well with a USP either, no offense whatsoever.
On a personal note: I learned to shoot DA well by shooting a Glock. Now, I am not pushing a Glock on you. They are not my favorite, HKs are. But I do like them and learning their trigger well helped me to shoot DA well in general. Sort of like how people will recomend learning DA triggers on a DA revolver. You have to learn not to anticipate the recoil all the while applying more and more pressure to the trigger until it breaks. Once it does it should be a surprise to you and the last thing you knew was that the sights were aligned on target. I don't mean to be patronizing and if you already knew all this stuff please disregard and take no offense.