Would you rather be at a regional when the music stops or at a company that flies its own passengers? While turbine PIC is great, the industry has changed. NK training isn't that "rough" or disorganized in my opinion. If you can dedicate yourself to a training program (cooperate to graduate) and put distractions aside, then you will be fine.

Take the ULCC, especially if you can live in base. Focus on the training and if the music stops you'll make more career earnings and have a comfortable(ish) life compared to being stuck at a regional pondering what life would have been like if you took the ULCC job.