A notebook is not a lifetime purchase in the way a knife or a pan is. You will fill it and start a new one. But the right notebook becomes a system: consistent paper quality, consistent format, consistent behaviour with your preferred pen. These three are the ones worth knowing.
Leuchtturm1917
The Leuchtturm1917 A5 Medium is the most complete notebook available at a reasonable price. It has numbered pages, a table of contents, two ribbon bookmarks, an expanding pocket, and a pen loop. The paper is 80 g/m2, which handles ballpoint and rollerball ink well but shows minor bleed-through with wet fountain pen inks. Available in over 20 colours and four layouts (blank, ruled, squared, dotted). It is the right choice for anyone who uses their notebook as a system rather than just a writing surface.
Moleskine
Moleskine has the strongest brand recognition but the weakest paper of the three. The 70 g/m2 paper bleeds with most fountain pens and many rollerballs. The elastic closure, back pocket, and hard cover remain well-executed. For pencil, ballpoint, and light fineliner use it performs adequately. At the same price as Leuchtturm, the paper quality makes it hard to recommend unless you specifically prefer the Moleskine aesthetic.
Rhodia Webnotebook
The Rhodia Webnotebook uses Clairefontaine paper at 90 g/m2, the best paper of the three for fountain pen use. There is no bleed-through with even the wettest inks. The trade-off is fewer features: no numbered pages, no table of contents, fewer colour options. At a lower price point than Leuchtturm, it is the best choice for fountain pen users or anyone who prioritises paper quality above everything else.
The Recommendation
For a complete notebook system: Leuchtturm1917 A5 dotted. For the best fountain pen paper at the lowest price: Rhodia Webnotebook A5. For pencil and ballpoint use and brand preference: Moleskine. If you use a fountain pen: avoid Moleskine entirely.