Frame vs. slide decocker & also DAO

Repost from general discussion forum...

I've never had any semi-auto pistols with a decocker. Aside from the obvious difference of location, what is the difference whether the decocker is on the frame or the slide. I guess I could see that if you were decocking it on the slide and something happened it could fire and the slide could tear your hand up or something. Can this even happen or are their safeties built into the decocking system?
I am wanting a conceal carry gun and I want to carry one in the pipe, from what people have told me the decocker is the only way to go, what do ya'all think? Any opinions of frame vs. slide models?
To be more specific, I am looking at the S&W 10xx series of 10mm's. (thanks offeror )
On DA hammer models I assume you can manually pull back the hammer and have a SA trigger after that? Does it go back to DA after firing or does the hammer stay back for SA mode?
Also, people claim that DAO semi-auto's are safer than DA/SA models. I have a Glock, and while I guess I can see with the longer and heavier trigger pull it might help slightly, I think overall accuracy (at least for me - I shoot SA a LOT better than a heavy DA) would suffer.
As you can likely tell, I've mostly shot SA semi-auto's and plain-jane DA models like the Glock (which I like, but not for concealed carry), and DA revolvers.
Opinions, facts or hear-say is welcome.