A loaded question. I've used my .300 win mag a lot but it's kinda silly as a dedicated deer rifle. Nonetheless it's my all game all purpose all distance rifle and I'm fond of it.
My .270 has taken the most deer. I've had it the longest. It works. The 270 Winchester is the cartridge against which all other dedicated whitetail and mule deer cartridges are judged in my book.
My present love interest that I'm most excited to take deer hunting in November is a Weatherby vanguard in .257 Weatherby magnum.
For brush hunting or other close range, rough use, and fast handling situations my iron sighted husqvarna 8mm mauser or borrow my dads marlin 336 30-30.