Uniqlo 3way

Specs
Reviews put it as well-made and reasonably sturdy
 * Cordura fabric
 * 500g (17oz) weight
 * 20-25 litres capacity (roughly 21L)
 * Dimensions: 45x31x12 cm OR 17.7x12.2x4.7 inch
 * Only 40 USD
 * Looks: Understated, business-appropriate, minimalist, black

Cons

 * Slightly on the smaller side
 * Briefcase handles stick out when carrying in backpack mode