It all depends on your decisions when you do any of the 4 things. College just typically has better overall options that don't end up poorly, lol. Going to a state school and getting an engineering degree will lead to a good income and low debt, but going to a private school with a low paying degree will result in high debt and low income.
The one thing about degrees like electricians is that they all scale really well if you're a hard worker. You can literally make yourself more successful by working harder and smarter than everyone else.
That doesn't really apply to a lot of college degrees. College degrees will get you good benefits and a good job at a corporation, but no matter how good you are compared to everyone else there's going to be very little financial difference.
I personally think that the trade schools currently have the best ROI now that college costs have gotten out of hand. Most of the those people are in short supply, electricians, plumbers, etc can make really good money if they're hard working.
That's really what determines whether the investment is worthwhile anyways, work ethic. Work ethic is the multiplier of the investment you've made in yourself. Doesn't matter the investment, whether it's college, books, etc, if you learn skills which are in demand and are able to provide them, you're going to be successful.
The funny thing about the poll is that if you drew a line on a graph that indicated 'success', the college grad band would all be banded closely around it. The tradesman would have a much wider band, where people either make a lot less than college or way more, depending on how hard they work. Real estate would be even more spread out, and the stock market would have the highest spread...if you picked a stock like Amazon or Apple 15 years ago, it would have easily destroyed any other investment. Of course, if you picked Sears it would have been the worst investment. :)