Another 136th and I-25, Thornton dweller here. According to RTD, light rail will be completed to 124th and Claude in January 2018 (call me skeptical)

Taking the 120X from Wagon Road (120th and Huron) is pretty convenient to downtown if you will be there all day. If it were me, I would probably look in Westminster to take advantage of Federal or US36 to get into downtown a little faster.

Just don't accumulate a whole lot of stuff. If you hate the apartment move when the lease is up. You really won't know if you like a place till you live there.