Mile 0 of the Alaska Highway is Dawson Creek, British Columbia.
Officially, the Alaska Highway terminates in Delta Junction, Alaska.
The Alaska Highway has undergone many improvements in past decades.
it is good driving with most of the highway being at least two lanes and paved.
Regardless of the section of highway, take your time and enjoy the scenery!
The section of highway between Destruction Bay YT and the Alaska Border has frost heaves and can be rough. The best advice is to slow down and plan 4-5 hours if you're driving an RV through this 100-mile section.
1956 Guide to the Alaska Highway (pdf), saved for decades by Jack Stalberg (my dad!)