The 124 has more energy, while the 147 has more momentum. Check out the following home video tests on each round.
124 grain +P HST: http://www.youtube.com/watch?v=COVoB...ure=plpp_video
147 grain HST: http://www.youtube.com/watch?v=PNRqr...ure=plpp_video
I'd say you get similar performance from either. I load the 124 +P's into my Glock 26, which is my carry gun. For that short barrel I prefer the lighter bullet in +P form. At home I go with the 147's in my Sig P226, which sits on my nightstand. All else being equal, and they are pretty close, I'd rather keep the round that won't be as loud in the gun I am more likely to shoot indoors. If I carried a gun with a longer barrel I may go 147 as well since the bullets hold up better against barriers like car windshields. Although I don't know that I'd ever be shooting through a windshield in a self defense scenario.