Honestly, all the answers on this post were correct (given that each caliber is used within its limitations) And to be quite truthfull, there probally isn't a (best) caliber that will ever be agreed upon. here is a list of calibers that can be used for deer. (some states do not allow certain calibers, so check with the laws first) where I hunt in new york...a caliber of .243 is the smallest that we can use for deer. So lets start with the .243

.243
6mm
240 weatherby
250 savage
257 roberts
257 weatherby
25-06
6.5mm
260
264 win
270 win
270 weatherby
280 win
284
7mm
7mm ultra mag
7mm stw
7-08
7-30 waters
30-30
300 savage
300 win mag
300 ultra mag
300 weatherby
308 win
30-06
303 british
303 savage
32 special
8 mm
338 win
348
358
35 rem
35 whelen
405 win
444 marlin
450 marlin
45-70 gov.
45-90
45 cal. muzzleloader
50 cal.muzzleloader
54 cal.muzzleloader

find out what your applications are and go from there. you have quite a list to choose from. (and there are even more cals. that u can use for deer) even though not on this list. good luck huntin I hope you choose the right gun for you