QOL is based on seniority, so if money is no object, where will you be senior the fastest? Hire on with a rapidly growing regional and stay First Officer forever... be off reserve in a couple months, hold a decent line in a year, and in two or three years be senior enough to pick your trips, overnights, days off, holidays, etc. I dunno any major where you'll get that senior that fast.

That said, there are always other considerations:

Will you mind flying around with age twenty-something Captains?

Is your regional diversified enough to stay afloat when its major(s) want to reduce your flying or find a cheaper vendor?

Does your regional have a strong union / good workrules, or do the senior guys get shuffled around just like the reserves?

Where can you fly free with your parent airline? London? Berlin? Hawaii? Tokyo? Or just Chicago?

Will you have to spend a day commuting on each end of a trip?

Is your regional run by a bunch of crooks who will raid the cookie jar in the dark of night and leave the pilots holding the bag?

And if money isn't a problem now, will it be in 10 years when you're only making $40,000 a year?