Looking for advice from those who have been there, done that....

I am currently employed at a regional that I've worked at for 4 years now, and have finally racked up 500 or so hours in the left seat. I have some PIC turbine from flying 135 before this. But, I am half way to being able to "check the box" on some majors 121 PIC requirements, and I'm beginning to struggle with where I should go from here. Meaning should I stay or should I go. I can stay here for another 6 months and get the rest of my 1000 Part 121 PIC, or jump ship and start building seniority at whatever legacy airline might take me.

I know that just because I start submitting apps, it doesn't mean the phone will be ringing off the hook tomorrow. And even if it did, I'd still have to do well in the interview and get the offer. I also know that just because you can check the box, it doesn't mean that you're going to get the call. But after watching friends around me with less time & experience get interviews and jobs, you just never know.

It's just that all this talk about mergers and consolidation and seeing what has happened to those before me---I can't help but be a little nervous about the "what-ifs." What-if I put it in and for some freak reason I get a call from Delta, NW, or UAL? I'd be dumb at that point not to take the shot. But what if whomever it is merges with someone and I'm on the street...it'd be nice to be able to check that box and have the option of applying at UPS, FedEx, SWA. With my views of the airlines having all changed, I don't really see any as truly better than the rest to call it my dream airline.

I also know you can't plan for everything, but I'd like to be as prepared as I could be. So, it would seem that getting the time would be the smartest thing, but is it worth passing on the potential seniority?? What would you do?? I know times are changing, but what did YOU do??

Thanks for your serious advice and opinions!