TL;DR. Two $0 Chase business cards designed to be held together. Ink Business Cash earns 5% on office supplies, internet, cable, phone (combined $25k/yr cap), 2% on gas and dining ($25k cap), and 1% on everything else. Ink Business Unlimited earns flat 1.5% on everything. Cash wins on category spend; Unlimited wins on catch-all. Both are best held with an Ink Preferred or Sapphire to convert cash back into transferable Ultimate Rewards points.
The three dimensions that actually decide it. First, category alignment. If you spend on internet, phone, and office supplies, Cash's 5% is the highest small-business return on those categories anywhere. Second, catch-all. Unlimited's 1.5% beats Cash's 1% on non-bonus spend. Third, point conversion. Both are technically cash-back cards but their "cash back" is actually Ultimate Rewards points (1 = 1 cent), which combine with Ink Preferred or a Sapphire for transfer access.
Real customer scenario for each. If you run a small business with $1k a month in internet, phone, and office supplies, Cash earns $50 a month at 5%, $600 a year, on those categories alone. If instead your spend is mostly non-bonus (contractor payments, equipment, miscellaneous), Unlimited's 1.5% catch-all is the better single card.
The trap to avoid. Holding only one when both are free. The standard "Chase trifecta for business" is Cash plus Unlimited plus Preferred. Cash for bonus categories, Unlimited for everything else, Preferred for the welcome bonus and transfer access. All three combined cost $95 a year.