I agree with everyone above saying to do it about whatever you personally like. You have to really have a passion for what you'll be talking about or you won't last on YouTube.
I want to add too that you should try and niche it down to focus on a select group of people. With my previous channel I made it way too generic (It was a generic tech channel) so as a result it was growing, but that growth was very stagnant. I'd recommend getting as specific as you can with your channel, for example instead of making a car channel (totally random example), you could make a car channel focusing on budget cars, or to go even more niche you could do a channel about creative ways of upgrading budget cars (as opposed to ones about their history or VS videos between them and more expensive cars and other videos). By doing this when people who fit into that specific niche find your video they'll be more likely to subscribe as they feel it's perfect for them, as opposed to no one feeling like they'd fit in with your channel if you do a really generic one.
Also try not to be discouraged by the low numbers you'll be getting at first, I started my new channel around a month ago and am getting very low numbers on it as compared to my previous channel. If you're determined enough, and enjoy what you're making enough, you'll eventually start to see growth (I even have to keep telling myself that now too, it is really hard when you're just starting a new channel). This is again why it is so important to love what you're doing, it should be your passion for whatever you're talking about that keeps you making videos, not the numbers or the potential funds.
I'd also recommend subscribing to Tim Schmoyer (Video Creators), Derral Eves, Video Influencers and Roberto Blake on YouTube. They are really great people to get tips from when it comes to anything YouTube.