Buy the Under Armour Womens Undeniable Signature DuffleDISC.

It carries an actual gym kit, the Nike Brasilia carries your shoes and a prayer.

What was compared

1. Packs a whole kit, not just trainers
The UA DuffleDISC holds 31 litres with a vented shoe compartment and mesh side pocket, room for a full change of clothes plus shoes. The Nike Brasilia is a single-compartment drawstring sack sized for light gear. Unless you only ever sling in a pair of trainers for a quick run, you will outgrow it fast.
2. Sweaty gear stays away from clean clothes
UA gives you a vented shoe pocket, a mesh side pocket, a front zip pocket and elastic straps for a yoga mat, four separate jobs handled. Nike's Brasilia has one interior divider and a single zip pocket, fine for keys and a phone but not for sorting actual gear.
3. Comfortable on your shoulder when it is full
UA's adjustable, padded shoulder strap and web grab handle carry real weight without digging in. Nike's Brasilia relies on thin drawstring cords, the classic sackpack weak point once you load more than a towel and water bottle.
4. More bag for less money
UA lists at $15.99 against Nike's $25.00, and the cheaper bag is the one with more capacity and more pockets. Paying more here buys you less room, not more.
5. Yes, Nike has the better star rating. It is not the better bag.
Nike sits at 4.8 stars across 7,602 ratings against UA's 4.6 from 121, but a sackpack with one job collects fewer complaints because there is less to go wrong. Judged on what a gym bag actually needs to do, carry a full kit and organize it, UA wins the comparison that matters.