Hwy 14 would be much better. 14A is pretty steep and winding -- not recommended for towing much of anything. As mentioned above, Hwy 16 out of Buffalo would be a little easier than either one. Some will suggest going through Billings; I wouldn't unless mountain driving scares the bejesus out of you. It's much longer, and Hwy 16 is pretty easy -- a nice scenic mountain drive on a good highway. I've also been over Hwy 14 several times. I don't consider it a bad road at all, but mountain driving doesn't bother me. I enjoy it and have been driving mountains for most of 50 years.