A shoulder bag is the most used object most people own and it gets chosen the most carelessly. I have watched people spend an hour on a sweater and thirty seconds on a bag they will carry every day for five years, so this issue is the version of that conversation I wish I had had earlier.

Start with the strap, because it decides everything. A shoulder bag needs a drop that clears your body cleanly, roughly 20 to 24cm if you want it under the arm and 40cm or more if you want it at the hip, and a thin chain will cut into you within an hour no matter how good it looks. Then the leather. Smooth calf shows every scratch and looks better for it, grained leather hides wear and is the practical choice, and a nappa or matelasse quilt is soft and will slump once it is full. Then the hardware, where I want solid brass or plated brass rather than anything that feels light, and a zip that runs with one hand. Last, the base: a bag with feet or a structured bottom stays out of the category of things that look tired.

Forty bags below, all from Net-A-Porter, across shoulder bags, suede, totes and a shopping list that spans about $255 to $5,250.

Below, starting with the house that made this shape its own.

Saint Laurent is the reference point for the leather shoulder bag and the range within one house is the reason it earns the section. The Cassandre matelasse is the flat quilted envelope, the Loulou is the softer chevron, and the Le 5 a 7 is the long slouched hobo that I think will outlast most of what is in this issue. The Mombasa is the archive shape with the horn handle, the Icarino is a quilted tote, and the Gaby Vanity is the small structured one for evening. If you want the practical outlier, the Sac de Jour Nano is a tiny tote you can actually put things in. Roughly $1,500 to $4,500.

The core grid. Valesque's Corset quilted satin shoulder bag is $255 and the reason I always tell people to look past the obvious names. Bottega Veneta's Knot in intrecciato green is the colour I would buy, Loewe's Joya is the hard sided evening option, and Gucci's Camera Case with the Web stripe is the most recognisable bag here. Chloé's Marcie in snake effect leather is the one for someone who has enough black, Vivienne Westwood's Dolce Medium Orb is the value pick at $1,110, and Saint Laurent's Nolita and Loulou Medium round it out. Note the range: $255 to $3,100 in one grid.

Suede changes the register of a bag completely, from formal to something that looks lived in from day one. Tory Burch's Romy is $395 and the entry point I would recommend without hesitation. Nili Lotan's Jagger is the clean navy crescent, Acne Studios's drawstring is the slouchiest thing here, and Tom Ford's small suede shoulder bag is the most polished. Métier's Tilt 22 is the quiet luxury choice, Saint Laurent's Loulou Mini in suede is the small one, and Valentino Garavani's Panthea and Tod's Bauletto both mix suede with leather trim, which is the construction I would look for if you are worried about wear.

A tote is a shoulder bag that admits what you actually carry. Dragon Diffusion's Rosanna Mini is $500 and woven by hand, which is remarkable at that price. Loewe's Flamenco is the drawstring that collapses and reopens, Bottega Veneta's Pinacoteca and Hop are the intrecciato options, and Savette's Symmetry is the most architectural. Toteme's belted croc effect is the one that looks like a work bag without looking corporate, Gucci's Bamboo 1947 is the heritage pick, and Khaite's Joan is the large soft one. Check the shoulder drop on all of these before you commit.

Eight more that did not fit a theme and deserved to be here anyway, from about $260 up. If you are buying one bag this year I would take the largest thing in this issue that still sits comfortably under your arm, in a grained leather, in a colour that is not black. Everything links straight through to Net-A-Porter.

Care, quickly, because a bag is the item where it pays off most. Empty it once a week, which sounds like nothing and is the single thing that stops a bag deforming. Store it stuffed with tissue in the dust bag it came with, standing up, not hanging by the strap, since a hanging bag stretches at the anchor points. Keep suede away from rain and treat it with protector twice a year. Do not use leather balm on matelasse or nappa, it darkens unevenly.

The other thing I would say is that resale value is not a reason to buy a bag, but it is a reason to buy a well made one. The shapes in this issue that hold their price are the plain ones, in the houses' own leathers, without seasonal hardware. That is also the bag you will still want.

Phoebe