257 Caliber. Close second is .277. I had a love affair with a Winchester Model 70 in 25-06 for about 25 years. Had a 270 win I used as well but it wasn't quite as accurate. Switched to a 270 WSM with a 1:8 twist. Amazing!
My favorite is whatever I feel like grabbing from the safe. I have a 300H&H, 270WSM, and 270 Win that need to see some blood. I'm sure the 300 has killed it's fair share of animals in it's life but since I've had it it hasn't drawn blood.
In the Adirondack woods my, long running favorite is .300 Savage. It's a great cartridge for minimizing deflection in the brush, but still flies pretty well. My longest harvest shot with it is 150 yds. My average shot distance with it is probably 50 yards. I've used .308 for longer shots, but am strongly considering a 6.5 CM or PRC for future open terrain.
Favorite cartridge? .308 for shorter range work, 264 WMI for reaching way out there on deer size game. For Elk size game way out there soon to be 300 NMI.