Of the three choices given, it would be 260, 243, 257, in that order.
I have shot a 243 a bunch, and used to use it a lot for deer. Then I got a 7mm-08, and it basically replaced the 243. I just feel a little better with the slightly heavier bullets (140 vs 100). Since you said nothing bigger than your choices, the 7mm-08 is out, but the 260 Rem is so close you'd never know the difference. Matter of fact, if I didn't have my 7mm-08, I *would* have a 260. They are just enough ahead of the 243 to really notice. However, like I said, I've shot the 243 a bunch, and still really like it. Lastly is the 257 Roberts. I know it has a big following on this site, but it has never done a thing for me. (Actually, there is only one 25 bore that I'd ever even consider, and it's the 250 Savage. Why? Who knows?)
So there it is, trying to stay within your guidelines and choices, while using a few other cartridges as comparisons for why I chose as I did.
