> Another is using smaller font size to make more info visible at once

This doesn't sound very usable to me.

You might be the kind of person who does benefit from accessibility features such as larger font size. On the other hand, I'm not; I can read 10pt font on 100 DPI display just fine, without glasses. I'd rather have an extra column in table view visible without scrolling than larger letters, but for you the tradeoff might be different. That's why it's accessibility and not usability. Usability would be if the bigger font didn't push anything off screen, then of course it's better to make it bigger.

Everybody has some minimum text size they're comfortable with. If you make the text bigger than that, they're forced to scroll unnecessarily, which is less usable. But the size differs from person to person, so it should be configurable. You get this automatically with web browsers and most GUI frameworks if you don't go out of your way to break it (just stick with the default font).