When I had one, I'd spend on it, and each day transfer funds to it to pay it off completely. I was spending something like 4x my credit limit per month, but because I was never over the limit at any given time (due to also making these payments) it was never a problem. Meanwhile, dem reward pointz...
But nowdays, I figured the rewards weren't worth the fees, and so I've gone back to just a debit card.
Disclaimer: If what I've heard about US banks is true, you probably WILL get in trouble and hit with over-limit fees / interest or whatever if you try what I did, in the US. Banks are a bit nicer here.
Also note, having one or the other is pretty much essential here. No one bothers with cash anymore, and some shops are starting to refuse cash over a certain value. Also, in the case of debit cards, they're $5 per year, or possibly even free, depending on the type; with almost no other fees (there's something like a 20c fee for using a different bank's ATM, that's pretty much it). The ones that you can actually use online / etc as if they were credit cards cost the $5; ones you can only use at ATMs or POS terminals are free.
A lot of places will waive the fee if you call/ask. If not, you can always downgrade the card. There's always the fraud protection/extra step in between your liquid assets by using credit over debit.
Debit cards get the same fraud protection as credit cards here. There really isn't any difference in practice, except for fees, reward points, and whether you're spending against money you've got in your account or a line of credit. ---