Quandry

I'm in a bit of a quandry now.
Since I quit on Friday I have done nothing to find a new job. Half-hearted looking at job websites hardly counts. I am still debating whether I should call my old boss and ask for my job back (not the one I just left but the one in the empty building). I'm sure that they would have me back, as they were always running short staffed and they seemed to like me. I could probably be back at work by the weekend if I pushed it.
To confuse matters, I received a letter in the post today from another company that I wrote to, when I sent off seven letters at once to local companies asking if they had vacancies, and they have arranged an interview for 6th March. So I don't know what to do now! DO I hold off for an almost certainly better paid job, and risk having another episode like Friday's. Or, do I go back to my old job and just get paid a low hourly rate, but in a place where I just risk being bored.
I think I know the answer, but I hate wasting opportunites.