Well I'll give you my .02 for what it's worth... If your ultimate goal is 121 major/legacy then I would say go with a regional 121. I say this for several reasons, but the biggest reason is that whether you want to end up in 121 or 91/135, you need to gain experience to get the good jobs. Sure taking a job flying the turboprop and getting 300 hours p/year of TPIC is awesome, but TPIC in a King Air hasn't landed many people from the 91/135 world a job at a major airline. The only couple guys I know personally who made the jump from 135 to 121 were both in management positions, and both had former military time flying fighters. I know one guy who got an interview after 5000TPIC in an Excel but he received the thanks but no thanks letter. Build time now, to get a good job later. A job flying only 300 hours sounds great when you have been at this for 8 to 10 years and have over 4,000 hours. But at less than 2,000 bite the bullet and get the hours.