I use Speer bullets but I use the Grand Slam in .270 Win 130 gr for deer and elk.
For whitetail just about any soft point 130gr .30-30 bullet should perform well. For deer you don't need to get too picky as far as bullet construction goes. Any standard soft point in the appropriate caliber will do, but I'm sure you'll get a slew of varying opinions now that I said that.
Anyone who shoots a sabot bullet has had the problem with loading the next round with a dirty barrel we have all struggled with it.
Between muzzleloader shots I have done some research and testing on my own to find out what works for me for the next shot. I have been using a product called bore butter and when the muzzleloader is just sitting around I leave it caked in the barrel for protection. Have also found that if I lube my sabots with bore butter they really slide nicely down the barrel....