Which of the two is less likely to cause scratches on my lexan windows? Is there a better choice? I realize the scratches will depend on the method of removal, so I guess the question really is: which one comes off easier?

They make lexan specific stuff in all kinds of colors. Jegs or Summit.

Dial Rite is what you want. Summit and Jegs carry it in various colors

The dial in chalk is way better to use on Lexan than any brand of shoe polish I have used
Pledge furniture polish, liquid or spray, works great on cleaning and polishing Lexan also, that is a old pilot trick taught to me at the airport on my airplane instead of buying the expensive Lexan cleaner sold at the airport shops and from small airplane internet vendors
That may not work on Plexiglas though, maybe it will

I found isopropyl alcohol helps remove stubborn shoe polish and window chalk. It melts it off and minimizes rubbing. Did not seem to hurt lexan when I had my old bracket Challenger.