I started with a SUPER tough niche, that site has never made a dime, but I took what I learned from that and built another site in a difficult comp niche, I got it to page 2, then realized I was over my head. I let those sites sit around, uploaded content occasionally and sat back and reassessed my goals and desires.
I then picked a broad keyword niche, like "starting a business". I began building content for super low comp stuff and getting that ranked, then I would build to a slightly less easy keyword, then on and on. I now have an authority site that is used by others to reference and talk about in that niche. I monetize it through Adsense, Amazon, Click bank, and affiliate ads. I am currently starting a new authority site build around the same idea.
I said all that, to say this: fail. Don't go for something because you are worried about failing, or you will already fail.
If the domains you have are good, buy a cheap, brand new name, do your own niche selection, find your own keywords, build your own backlinks for tier 1(don't automate). Fail. Analyze what you did wrong and start over, get another cheap domain. Apply this principle to whatever method you decide to go for it. Fail, try again, stick with it and you will make it.
OP: if you want to build a site, and monetize with Adsense, I will give you a seed keyword to start with that has a comp score of 11/100 on keyword revealer.