Another $.02
My opinion is worth every penny you paid for it, but...
As someone who went straight from AMF (6 1/2 years) to a "major", this is what I learned from the experience:
1. For the average pilot, I don't believe there are really any shortcuts to the final goal. Still know your training partner who soloed the day before you? You'll probably be at his/her retirement party the day before yours. Sure, there are those "blessed" individuals who have an inside track past all of us all the way to the top, but if you were one of those, you probably wouldn't be asking us for advice. My point is that (at least for me) this is more of a journey than a destination. Stop counting every click of the hobbs and enjoy the ride! You'll get there.
2. Keeping #1 in mind, I suggest you focus on where you want to be and what you want to be doing right now, vs. where you think it leads. The flying at AMF and SW are very different, each with it's high and low points. If you'd rather be at SW, then go there. If you like the flying and schedule at AMF more, stay where you are. The majors will still be there when you are ready for them...
3. Many percieved "fast routes" really aren't. Noone has a crystal ball that can acurately tell you the best route, especially in this industry. Many of my instructor buddies who went to the regionals at the same time I went to AMF thought I was nuts. Most of them are still at the regionals, some still right seat (0 pic). I upgraded to the SA227 really fast because all the senior guys at my base turned it down so they could go to the regionals (didn't want to sign the 1 year thing). Two years later, many of those guys were calling me for a job because they had been furloughed (9/11). My point is you never know...
4. Whew, this is getting long. Finally, don't forget that this undustry is pretty tight and your reputation will follow you wherever you go. Sure, you didn't sign a legal contract, but did you lead anyone to believe that you would stay at AMF for any length of time? If you did, I would suggest that you earn (and keep) a reputation as someone who is good on your word. If you don't, this will bite you one way or another. If not, you are free to do whatever you want. Just be up front and honest and you'll never regret it...
Sorry that was soo long. Hope it helps. Good luck!!!