I could not answer that question because too much depends on the person(s) doing the trip. I have never cycled the Transam route, but I have read quite a few journals written by those who have. Judging from what they said and from the photographs I have seen, I would say the TA route would be your best choice. Then again, the pacific coast route is really great. The atlantic coast is ok, but the pacific coast has it beat by a long shot, in my opinion. The southern tier I have done a number of times in its entirety, and also half way a few times or so. The ST is good if you want to see western states. I say that because I am from the east, which to me is old hat. It also gives you a major change in terrain, but so also does the northern tier. As for meeting people, I guess that kind of depends on you and who you meet. Just about any long cycling tour anywhere can be pretty good. It does not necessarily have to be along a specially mapped route. You could also try just wandering, meandering with no particular point to reach at any time. Just go wherever you feel like going day after day. That was how I started bicycle touring. No point A or point B. Just start when you want and stop when you want. However, some places are better for cycling than others.