Hello 4dr, and welcome to the DRTV Forum. None of us here will ever get tired of discussing .45's. (If anyone says they do, they are lying.) Since you narrowed it down to three, but listed four, we'll go with that.
All the ones you listed are full size, and have their pros and cons. IMHO.
Start in reverse order HK.45 : Sweet and overpriced. Not the best reports of customer service.
FNP .45, Nice right out of the box, reliable, priced right, but it is BIG. (FWIW, I have the FN9, Not 1 issue ever,..)
SigP220, Know the customer service is great (Sig556 rifle owner), but the best I can offer is this review. Little overpriced but read the review.
http://www.christiangunowner.com/sigsauerp220.htmlXD-45, It's a Springfield, Out of the box reliability, it was a toss up for me between the XD-40, and the M+P, I chose the M+P for the ambi features, and the grip felt better to me.
Did you look at the M+P .45?
With ammo prices the way they are for .45 I would go with the FNP, or XD, you do not get any extras but higher price with the other two.
Just my .02 cents. Ultimately it's up to what fits your hand, eyes, weight, and features, FOR YOU. Good list.
What do you plan for your choice? SD, competition, CCW, ? Let us know it will help.
TW