ORIGINAL: zrexpilot

The question at hand is a varmint round with occasional deer,
which is better for deer is very arguable, they both shoot pretty small pills 100 gr. and 115 are the most common, not much difference and a deer wouldn know it either. For varmints the .243 will have the edge because of the smaller bullets readily available. The .25's are just not that popular, and ammo is harder to find. If you dont handload the .243 is the way to go, ammo is available everywhere ranging from 55gr pills all the way to a 100gr.
The .243 with 75gr bullets are terrible medicine for varmints. The .243 does indeed have less recoil, if that matters, it has the shorter action, which some say are more accurate. The .25's are vary rare in competition shooting, but the .243 wins all the time in 1000yd matches I wonder why that is.....Hmmmmm. The .243 has the the higher coefficiency .Yep I say go with the .243
Actually if you handload the .243 is still the way to go, loaded up they are smoking hot.