Okay so.... lots of questions for YOU
Did you leave your old job out of spite? because you didn't get the position you applied for? because they weren't paying you enough? because the new position was more money? the new position was more the kind of role you're interested in?
I think this is more a question of "is your old company worth going back to?" because if you hated it then, you might hate it still. Regardless of the new position and POTENTIAL for more money.
Does your old boss suck? Compare the cultures of both companies. I've worked quite a few jobs all very different from each other and the only thing that was consistent is if the company culture was positive, I enjoyed my job. I excelled. I made money. I grew. If the company culture was trash, I hated everyday (still excelled - obv).
I think your biggest deciding factor should be how you felt/slept/lived while working at your old company compared to your new one. Has having this "new gig" been better for you as a whole? Is this new position/role/title more in line with where you see yourself in the future? Is there growth opportunities with this new company that you're maybe not seeing?
I only would leave a job if I wasn't happy there so FOR ME it seems like you already made the decision.
If you really can't decide - compare the little stuff.
Which co-workers do you like more?
Who has a better (seemingly because I am assuing you haven't attended one yet) holiday party?
I hope you'll make the choice based on what SERVES YOU and your well being and not your bank account. Whichever company you go with - REGARDLESS - if you are unhappy in your position - leave it. Find a new path. Find YOUR passion.