In New York Magazine in November 1983, Yves Saint Laurent said: "I have often said that I wish I had invented blue jeans: the most spectacular, the most practical, the most relaxed and nonchalant." A couturier who dressed Paris for decades was envious of five pockets and a rivet. I find that very easy to love.

It also explains why YSL jeans make sense as a category. The house has had a few different hands on the denim since then. Hedi Slimane ran Yves Saint Laurent from 2012 to 2016, moved his studio to Los Angeles and dropped "Yves" from the ready-to-wear label. Anthony Vaccarello was named creative director in April 2016 and has been there since. Each of them cut the same pair of blue jeans a little differently.

Start with the straight and slim cuts, because they are the closest to what Saint Laurent was talking about. The Straight Jeans in South Blue and the 90's Slim Straight Leg are light and faded, and both are 100% cotton made in Japan. I would wear either with a white tee, a camel coat and flat boots in October. The 90's Mid-Rise Straight in Authentic Medium Blue has soft whiskering, so it already looks lived in. The Nico High-Rise Straight is the one I would pick for a sweater tucked in at the waist.

Two practical notes. The Slim Jeans fit small, so size up one. The Straight Leg Slim Fit in Chalk White is a bright, clean pair for early fall, but I would hold it for dry days.

Saint Laurent launched its ready-to-wear line Rive Gauche in 1966 to democratise fashion, and the baggy jeans here feel like a descendant of that idea: a plain thing made with real attention. A lot of these pairs are made in Italy, and you can feel the seriousness in the weight of the denim.

The V-Waist Long Baggy Jeans in blue are the headline. The waistband dips into a V at the front, which makes the high rise look sharper on the body. The Neo 90's High-Rise Baggy in Dark Summer Blue is sun-faded and loose through the leg, so it suits sneakers and a cropped jacket. The Neo '90s Wide-Leg is a relaxed mid-rise for anyone who finds a high waist fussy. For something darker, the Faded Wide-Leg in deep indigo has contrast top stitching and a leather patch at the back. The Nico Wide Leg in Berlin Black is long and straight, and it is the one I would wear with a fitted knit and loafers.

Test for the hem: stand in the shoes you actually plan to wear and check that the denim just skims the floor. A wide leg that drags in October rain is a short-lived pair.

What I would skip: the baggiest cuts if you are petite and have no plans to hem. Long denim is lovely until you are stepping on it.

These are the pairs that look best with a heel or a boot with a little height. Saint Laurent has always loved a long, lean line, and the flare takes that to the floor.

The 70's High-Rise Jeans in Dark Night Blue Rinse are the cleanest of the lot, and the same cut in Old Black is faded and wide at the hem. The 70's Authentic Medium Denim is fitted through the thigh and flares at the hem, and it is made in Japan. The Yves Flared Jeans carry a logo-embossed leather tab at the back, which I think is a sweet nod to the founder. Both Yves Flared and the 70's Flared fit small, so check the size guide before you order, and consider going up one or two. The Clyde Bootcut has a single center pleat, and it is the one I would wear with a pointed boot and a long coat. The Bootcut Leg in Indigo is a clean dark wash with a button fly, and the Almond Milk pair is creamy and slightly flared.

Fitting-room test: sit down. A high rise that digs in when you sit is going to bother you by noon. Then walk, and look at where the flare starts, because it should open below the knee, not at it.

What I would skip: the Almond Milk pair for rainy commutes. Pale denim in October asks for a lot of attention.

Dark denim is the quiet end of this edit. Most of it comes down to how the black has been finished: faded and soft, or inky and stiff. Read the fabric notes before you read the color name.

The V-Waist Long Baggy Jeans in French Black are faded charcoal, so they sit somewhere between black and gray. The High V-Waist Baggy Wide Leg in Deep Sea Black is washed and shown with a belt. The 90s High-Rise Slim in black is the narrow option, and it fits small, so I would size up two. For straight legs, the Relaxed Straight Leg in Old Black is inky and made from midweight denim. The Straight Leg in Ash Black is heavyweight and worn in, and the Nico Straight Leg in Black Dye adds a leather contrast detail. If you want something dark but not black, the Nico in Heritage Indigo is rigid denim with a slightly worn wash. The Slim Fit in Worn Black has a high waist and an ankle hem.

Pair the worn blacks with a gray cashmere knit and the crisp ones with a white shirt. I would wear any of them with a leather boot.

What I would skip: heavyweight denim if you want to move easily on a long train ride. It softens, but it takes a while to get there.

Pre-owned denim is where the Vaccarello and Slimane years sit side by side. Hedi Slimane is credited with the skinny black jeans look, and the Pre-Owned Distressed Skinny Jeans in light blue, size 26, are cotton and elastane made in Japan. Jeans from Vaccarello's 2018 collection also turn up, like the Pre-Owned 2018 Washed Blue Flare Leg Jeans in size 27.

The rest of the group is a mix. The Pre-Owned High-Waisted Slim Jeans in blue are listed in very good condition and are 98% cotton with 2% elastane. The Pre-Owned V-Waist Long Baggy Jeans in black are listed as new. The Pre-Owned D05 Washed Blue Tapered Jeans in size 29 are mid-waist and made in Japan. The Pre-Owned Dark Wash Straight-Leg Jeans in size US 26 list a 25 inch waist, a 32 inch inseam and a 9.5 inch rise, so you can check against a pair you already own. The Pre-Owned Distressed Slim Tapered in size 30 is a cotton-blend twill with a zip fly.

Before you buy, read the condition line, then check the hem, the pocket corners and the inside of the waistband for wear. Look at the leather patch and the button hardware, and ask for authentication papers if the listing does not show them. Sizes on pre-owned pieces vary by era, so trust the measurements.

What I would skip: a distressed pair if the distressing looks uneven in the photos. Real wear should look like wear.

I would begin with a straight leg in a mid-blue, because it is the pair that does what Saint Laurent described: it has expression, modesty and simplicity, and you can wear it a lot. If I wanted a shape with more attitude, I would go to the V-waist wide leg next, and then to a flare for a night out.

Whichever cut you pick, check the size notes first, since a few of these fit small. Try them sitting down, then walking.

Saint Laurent wished he had invented blue jeans. The next best thing is a pair with his name on it, and a closet that gets to use it every week.