Work bags used to mean one thing: a black tote that looked like it had opinions about your career and none of them kind. That's changed, and mostly for the better. There's more choice now in shapes that don't require you to also be in a trouser suit to carry them.
Fit is the thing nobody tells you to check, and it's the thing that goes wrong most. You want a bag that sits at the right height when the strap's on your shoulder, not one that swings at hip level and clatters against you on the stairs, and not one with a handle drop so short you're walking at an angle like you're carrying a shopping bag with a grudge. Try it with what you'd actually put in it, not empty. A bag that looks sleek on a hook can turn into a brick the moment a laptop, a water bottle and a cardigan for the office air conditioning go in, and then the zip won't close properly and the top gapes, which is its own quiet humiliation on a crowded train. Structured bags hold their shape better over the day but show every scrape; soft, slouchy ones forgive a rough commute but sag if you overload them, so check the base doesn't bow out like it's had enough of you.
It needs to go with more or less everything you wear to work across a week, which in practice means it shouldn't fight with your coat. A bag with a lot of hardware looks sharp with tailoring and slightly aggressive with a jumper. Stick to colours that don't ask a question every morning: a proper mid brown, navy, black if you want it to disappear, a soft tan if you want it to do a bit of the outfit's talking. Avoid anything with a finish so shiny it photographs better than it behaves, because that gloss is usually the first thing to crack.
Leather that's a bit stiff at first will soften with genuine wear, not with fretting over it, and will start to look better once it's taken a few knocks. Cheaper faux finishes tend to go the other way, cracking at the corners and the fold lines within a year, which is where most disappointment with these bags actually comes from. A damp cloth and a decent conditioner now and then does more good than any spray promising miracles.
No work bag, however good, will make a disorganised commute feel calm. That part's still down to you.