- CSS reset - completely reset all browser styles to be blank essentially, across different browsers, so then you'll build your styling on common ground
- CSS normalize - same idea of resetting to a baseline, but keeping some of the default styling but still make it consistent across browsers, so not stripping away everything
No, a browser's defaults are, well, its defaults. One doesn't reset to them.
I think the line between a normalizer and reset stylesheet is _very_ fine, if there even is a line. A normalizer is probably _slightly_ more opinionated than a reset stylesheet. In the end, the difference isn't really important. If you need a reset stylesheet, normalizer will probably do just as well.
No thinking involved at all outside of your normal design method. No need to investigate the latest trends or activities by some online guy. Just do what you do.
"Just". What I remember from that time was putting a button at relative 0,0 and it being at the top-left of the page in one browser, but was offset in another because that browser was adding padding/margin to <body>. I cannot say which was "correct" but it nonetheless pushed me to use normalisers, which prevented this kind of problem from ever coming up again.