My wife and I both grew up in Princeton Junction, and both our families are still there so we go back often, almost once a week. I just happen to live in Williams Township also, making me a perfect candidate to answer your question.
First things first, do not take I-78 into Rt. 206. Both highways are very bad with traffic. There is NOO way you will get to Princeton in the amount of time Google says you will. Maybe 1 hour and a half if you're lucky.
The best route to Princeton would be to take Rt 611 S and follow that along the river onto Rt. 32. Cross the river into NJ at Milford or Frenchtown take Rt 12 E into Flemington. Could take Croton Rd S so you can bypass Flemington and go directly into Rt 31 headed toward Pennington. Then take Rt 518 E into Hopewell, then Carter or Great Rd into Princeton. This route would get you into Princeton in just about an hour.
I've been doing this for more than 3 years now, so I've trimmed the route wherever I can to about 55min, but I don't think you can get there much quicker than that.
During off-traffic hours you could take Rt. 78 to Rt. 31 in Clinton, but even then I still wouldn't advise Rt. 206. Rt. 206 is almost always busy.
I've grown used to driving the route, but some people don't like it since there are many winding roads and can't just flip cruise on and run for 50 miles.
Given from what you had said about taking one lane roads, it's not ideal, but the good thing is most of these roads have little to no traffic.
Doylestown is good, but I think it takes almost 45 min from Lehigh Univeristy, and about the same or maybe even more to Princeton. I guess it's a more "central" location to both of your work locations though. I can't comment much more than about Doylestown.
Let me know if you have any additional questions about the Williams Township <-> Princeton commute.