I have semi's in .223, 6x45, .270, .30-06, .50 Beowulf, all of them work extremely well. That includes DPMS, RRA, Browning BAR's and HK SLB2000.
I have bolt actions in about the same number of calibers, all of them work extremely well.
I have only one single shot, Browning 1885 in 45-70, that I hunt with and it works extremely well.
Neither is better than the other, none is more sporting. The Semi's offer a slightly faster follow up shot, and I'm willing to meet anyone who is faster with a bolt action at American Shooting range to do side by side trials. The bolts are more often than not slightly more accurate.
Just pick what works for you and be done with it. By the way I've had plenty of second shots on animals, if it's not on the ground when I recover from recoil another is on the way. Even a perfectly heart shot whitetail can run 30-100 yards easily, I don't like tracking in South Texas rattlesnake country.