Here are my views on this and keep in mind this is like asking what tires or type of oil should I use?
Both roads are remote and will provide the trip of a lifetime.
The road to Prudhoe Bay is called the haul road for a reason. It will be primarily truck traffic. The road to Inuvik will have more automobile/pickup traffic than the haul road because it services a real community at Inuvik.
Prudhoe Bay is a working/oilfield town and caters entirely to the work environment. Inuvik is an everyday town with restaurants, hotels, convenience stores, library, touristy stuff, etc.
The scenery will be similar on both roads.
Both roads can have challenging spots if it rains or snows and can be down in the 30's even in the summer.
Distance from Coldfoot to Prudhoe is 250 miles between gas stops. I don't remember the longest distance on the Inuvik road but I don't recall it to be greater than 250.
Some simple rules: slow down for oncoming traffic. 99% of the truck drivers will show the same courtesy and slow down for you. Remember they are trying to manage energy on 80,000 pound rigs so if a trucker is on your bumper get out of his way as soon as safely possible. The other vehicles on the road are another story so you get what you get. Some will slow down others will not. I slow down because I know what flying gravel does and to minimize my own damage when others don't slow down.
Leaving from Fairbanks you will go on the Top of the World Highway which as of last summer has less than 30 miles of gravel all the way to Dawson City, Yukon. Dawson City itself is worth the visit.
In a nutshell: Prudhoe Bay is black and white and all business.
Inuvik is colorful and in my opinion more fun plus you will see Dawson City which is lots of fun!