RE: in your opinion, the best deer hunting caliber...
I use a .270 for deer. That said, I don't think it's the "best".
If I had to choose the ultimate caliber to use on whitetails...it would be like 3D said, the 25-06.
If you can shoot...and you hit a deer in the vitals....the following calibers are wonderful.
243
6mm
264
270
280
7mm
30-06
308
anything larger....too!