Their experiment was based on coin flips and self-reported happiness, but basically those who made the big change after the coin told them to reported being substantially happier, and if you dive into the data, you'll see that those that went with the biggest decisions (quit a job, get married) saw a double digit improvement in happiness.
Paper is here: http://www.nber.org/papers/w22487
I've made what seem to be four major career decisions in my life. Aged 14 at school I was in tears because I couldn't do one of the O levels I desperately wanted, the school pretty much forced me onto this new Computer Studies course they'd just started running. As a direct result it grabbed me and I worked in the games industry for a good few years.
In my late 20s a friend offered me a role earning a lot more money wearing a suit in the IT department of an insurance company. A very tough choice as I loved the industry but after a couple of weeks of heart wrenching I took it; absolutely no regrets 25 years later.
Now at work unless I can decide using experience or hard facts I'll either choose not to decide or do a coin toss. It infuriates some people but if I can't sensibly analyse it any more and my crystal ball isn't working that day then random is far better than wasting time thinking about it.
One other thing to help make a quick decision is to toss a coin and whilst it's in the air think how you want it to land and then go with that. The limited time forces you to choose what is generally the route you subconsciously want.
Either just do it, or just don't do it. Don't sit on the fence. None of life's decisions (save maybe jumping off a bridge) are anywhere near as irreversible as they seem when we're facing them, no matter what we choose, and the worst thing is to remain paralyzed and let both opportunities pass you by.
and making children
It takes years to measure the quality of a parenthood or a marriage.