What each is actually good at
A card is for buying things from suppliers who take cards: fuel, materials, software, travel. Pay in full within the grace period and the credit costs nothing.
A line is for cash — payroll, rent, a supplier who takes bank transfer only, a tax bill. Cash from a card means a cash advance, which usually carries a fee, a higher rate and no grace period.
Limits differ by an order of magnitude. Business card limits commonly run in the tens of thousands; lines routinely reach six figures.
Cost, honestly compared
A card paid in full monthly is the cheapest credit in existence, because it is free. A card carrying a revolving balance is among the most expensive.
A line charges from the day you draw, with no grace period, but at a rate well below a card's revolving or cash-advance rate.
So the comparison is not card versus line in the abstract. It is: paid-in-full card, then line, then revolving card — in that order of preference.
Qualifying
Cards are easier. Many are underwritten largely on the owner's personal credit, and are available to businesses far too new for a line.
Lines are the hardest of the four funding products here: typically a score around 600, a year or more trading, and consistent revenue.
The practical sequence for a young business is a card first, then short-term funding repaid cleanly, then a line once the history supports it.