I disagree that Szeth's Stormlight is weaker than the Knight Radients.
WoR Spoiler
We don't see anything in the books indicating that KR are actually better or stronger using the Stormlight they possess.
Given the inherent unreliability of Forgers, I would not trust them with my soul. I would need to put in the work to be able to verify everything they did, and at that point their work would almost be redundant.
I chose Scadrial assuming I'd be either a mistborn or ferochemist. If I wasn't allowed any innate magic I'd really rather stay here. If I was forced to chose, I'd probably go for Nalthis cause I honestly don't think I have the patience to learn the magic of Sel.