Which of these should I start?

Joe, don't imagine that the niches/markets with the most money in them are going to be the ones in which you can most easily make some money. The exact opposite is a far more likely outcome, and there are reasons for that (and they're pretty good and pretty reliable reasons, too!).

Key concept: contrary to what you might have read elsewhere, it isn't about "the size of the pie" - it's about "the size of your slice of the pie". That's what pays my mortgage and bills, every month. The only relevance to me of "the size of the pie itself" is that the bigger it is, the harder it's going to be for me to cut out any slice at all, let alone the big, rich, nourishing slice I want.

Niche selection, ultimately, is about whether you want to sell metaphorical "jeans" (huge demand, but everyone else sells them too) or metaphorical "skating videos" (small but enthusiastic market and very, very few other suppliers). Most people try to sell jeans "because that's a huge market with plenty of money in it". :p

In other words, they're making their decisions according to the size of the pie - and perhaps that's why so few of them ever really succeed. :rolleyes:

It's explained in more detail here: Niche Selection Roadblock

And here: Weight Loss Market: Still Profitable ?

And here: Most Lucrative niche in Internet Marketing?

And here: Guess who is going to have the most profitable business?

.