We use AMEX Blue Business card for our monthly purchases. We pay the balance each week and it allows us to get back just around thousands a year in rewards! We've also used the Capital One Spark card with the same benefits. The trick is to pay it each month and not carry a balance. With that being said, sometimes we've had to carry a balance if we had slow paying clients with a big job that required larger materials purchases, but as soon as we received funds from the client we settled the balance.
So long as you use the cards responsibly, using cards to leverage cash Flow in your business is a smart money move.
We did try one of those "no preset spending limits" and I didn't like that for us because an algorithm is deciding whether or not to approve the charge.
Hope this helps!
