I'm curious as to what the company is telling new hires about upgrade. I can tell you it will be a lot more than 3 years. My best guess for a new hire today would be 5+ years to 190 Captain.
As far as the planes, it's no contest. Pay, comfort, schedule, overnights, even hotels...it's the Bus, hands down. That's not even getting into the average life of a 190 FO...multiple legs, super-quick turn times, no food or rest during the day (unless you get "lucky" and score a 2 hour airport appreciation in your schedule), apologizing every leg for something or other, then you get to your layover and fight to get to an extremely remote hotel with (again) no food available. My advice: run screaming from any attempt to to put you in the 190.
Sorry to be so negative, but you should have the real story before you show up. It's a great airline if you get the 320...I sure wish I had picked the 320, and I'd hate to see anyone make the same mistake I did.