Whatever fits in your hand best.
Well, I guess it isn't quite that simple. Of all the .45's I've shot, 1911's are the softest shooting, likely because they weigh a ton. However, they also fit my hand very well. My P220, however, did not fit me as well, and as a result I felt more recoil and didn't shoot it as well. Consequently, it went into storage and was eventually sold. My XD-45 feels like it was made for me and I scarcely notice any recoil while shooting. When I first took it to the range, it shot so softly that my wife, who is somewhat recoil sensitive, was eager to give it a try. She got off four shots before clearing the gun and relinquishing it to me, rubbing her hand because the recoil was so uncomfortable. I guess my point here is that it's not just the mass of a gun that factors in to felt recoil, but also ergonomics.