What the number tells you
Paper weight is usually given in grams per square metre. It describes mass, not thickness, absorbency, or how a fountain pen will behave. Two sheets with the same weight can feel quite different because the fibres, pressing, and surface treatment differ. A heavier sheet may still feather; a lighter one may keep a crisp line.
For everyday notes, start with the pen you use most. A sheet that is beautiful with a dry pencil may be frustrating with a broad wet nib. Test a normal sentence, a dense patch of hatching, and a small dot held for a second. Those three marks reveal more than a smooth blank sheet does.
Read the back of the page
Ghosting is a visible shadow of writing through a sheet. Bleed-through is ink that has reached the other side. They are different problems. Ghosting may be perfectly acceptable in a thin travel notebook; bleed-through can make the reverse unusable. Check the sheet in the light where you normally write, not only under a bright shop lamp.
Run a clean finger across a test line after a realistic pause. Smooth, less absorbent paper often gives ink a sharper edge but asks for more drying time. If you close a book quickly, a small piece of blotting paper may help more than buying a much heavier notebook.
Keep a comparison page
Record the paper, pen, ink, and date on every test. Add a note about drag: does the surface give your pencil enough resistance, or make handwriting feel hurried? Compare the pages after a day rather than relying on a first impression. Ink can look quite different once it is fully dry.
There is no single best paper. The right choice is the one that balances portability, comfort, legibility, and cost for your actual use. Save a sample when you finish a book, and you will gradually build a useful reference rather than a collection of half-used purchases.