Not sure why you are asking the question - but if you are planning a trip some specifics might help.
When do you plan to do your trip? West-to-east or east-to-west?
Do you prefer more services or more remoteness? Usually it's one or the other.
Do you plan to ride with others or hope to meet up with other riders?
What is your touring style - mileage, camping or motels etc.?
I have always opted to create my own routes rather than squeeze myself into a set route.
In my nearly 100,000 miles of touring I've ridden nearly all of the TransAm and much of the Northern Tier.
I am not a big fan of the TransAm -
Kansas is brutal in mid-summer and Kentucky has lots of dogs.
Although there are frequent services, you're just yet another cyclist along the route.
The Northern Tier is much better temperature-wise in summer but has a shorter riding season.
West-to-east it starts out with some really tough climbing and limited services.
Then after Glacier National Park you have 1000 miles of Great Plains riding.
If you do plan to create your own route - you can piece together sections from ACA and others.
I favor riding further north in the summer for two reason - temperatures and bike-friendliness.
The Midwestern states are way more bike tolerant than the South.
Thus, I would lean to some variation of the Northern Tier with a few changes.
1) The Northern Tier sends you north from Iowa to Minnesota than across North Dakota.
Why not head directly west thru South Dakota where you can ride in the Black Hills -
Then head north from Yellowstone to Glacier in the Rocky Mountains?
(That would be the southern and western legs of a box rather than the northern and eastern.)
2) You may want to rethink the Washington section of the Northern Tier - esp. if you are just starting out.
It's really beautiful, but tough if you are new to touring or just a bit out of shape.
There are plenty of other great options in Oregon and Washington.
3) You can always start/end the eastern portion in southern New England or near New York -
Rather than all the way out to Bar Harbor, Maine (which is really touristy and expensive).
But northern New England and the Adirondacks are the best part of the eastern Northern Tier.