An a line dress suits almost anybody who wants to get dressed without a negotiation, which is most of us most mornings. It's kind to a bigger middle, it doesn't need you to have decided how you feel about your stomach today, and it works standing up or sitting down, which sounds obvious until you've spent a night in something that only behaves in photographs. The only people who might want to think twice are anyone who wants a dress to skim close through the hip and show the shape there, because that's not what this cut is for. It adds rather than hugs. If you're after close, this isn't your shape.
What I like is how little thinking it asks of the rest of the wardrobe. Flat boots and a denim jacket for the school run, the same dress with heeled sandals and gold hoops for something in the evening, a cardigan thrown over if the weather can't make its mind up, which in this country is always. I've got one I've worn with trainers to a car boot sale and with heels to a fortieth, same dress, nobody clocked it was doing double duty except me. That's the whole appeal. It doesn't need you to plan an outfit around it, it just needs you to pick shoes.
The difference between a good one and a bad one shows up fast. A disappointing one is cut from something stiff that stands away from the body like a tent, or the seams sit too high so the fullest bit of the skirt starts right under the bust and makes you look pregnant with a laundry basket. A good one drapes, has a proper seam at the natural waist or just below it, and the hem has enough weight to swing rather than flap. Check the zip too, a cheap metal one will catch on everything including, memorably, my own cardigan at a wedding. Little things like a lined bodice or a facing that actually sits flat matter more than anything printed on the label.
On colour, I've gone off block black for this shape because it photographs well and does nothing for actually being looked at by a person standing in front of you. A soft rust, a deep green, a dusty blue, all of these do more work and hide less. Prints are fine as long as they're not so busy they fight with the shape of the thing. Pale shades show everything, including the inside of a car boot sale, so I save those for days I'm not planning to sit on a kerb.
Mine get better with age, oddly. The fabric softens, the swing gets easier, and by the second summer the dress has stopped looking new and started looking like something you actually live in.