thats an interesting opinion on the difference between 121 and 91 PIC time, never thought of it that way. I have flown 121 and am currently flying Part 135 on demand charter, in my opinion you have to be much more on your game flying Pt 135 due to not having a schedule but still having customers who want to get to their destination, also unfamiliar airports are the norm, just went to some podunk airport in the middle of Wyoming on 30 minutes notice. Flying Pt 121 I felt that complacency can and does set in due to the same routes and not having to plan as much, but that is what makes it so safe, Pt 135 doesn't have near the safety record. I think that all types of Jet PIC are very valuable and you will learn tons If you are flying an RJ or a VLJ just get the PIC the quickest route available to you. Remember with the way the industry is right know we all may be at the same job for a few years so try to be at one that is at least halfway descent.
Just my opinion.