I am 21 now, I have used my debit card maybe... once? No... Twice!
I have had three credit cards for the past few years, never paid any annual fees nor any interest. EVERYTHING I buy is with credit cards and I pay it off every month.
Why do I have three credit cards?
Well because Credit Card #1 gives me 2% back on gas & groceries (was 5% for the first 6 months) - so I use it for... Gas and groceries! https://www.applyonl...c=COMP&lc=en_CA
Credit Card #2 is an SPC (student price card) there are a bunch of places that give you various discounts (such as 15% etc.) so if I am shopping at a place with SPC benefits... I use my SPC card http://www.bmo.com/h...nt-credit-cards
Credit Card #3 gives me 1% back on everything. So if I am not buying gas/groceries or getting anything from an SPC location then I use this credit card.
(Standard CC no point in me providing a link - pretty much everyone offers one similar to this)
None of the above have annual fees, and I probably get about $150 back per year. It's not a whole lot... but why not? What do I pay in annual fees? $0 What do I pay in interest? $0...
If I wanted to use my debit card how many free transactions do I get? 10
If I want to use more than 10 transactions on my debit card, what do I pay? $1/transaction.
However the debit card argument is null since there are obviously other debit card plans I could be on. I just chose the one I have because I never use it.
This said, some people have credit cards so they can get things they can not afford right now, and they just make the minimum monthly payments. Which is obviously not a good thing, as long as you pay off your credit cards on time every time, there is no disadvantages to having one, again, unless you happen to splurge and buy more than you can afford.
Edit: I actually have a fourth credit card. Again no annual fees... It's a Scene Visa Card... I got it because it came with 3 or 4 free movie theater tickets (in the form of scene points)... Then whenever I go to the movies I use that credit card because I get added benefits... I rarely go to the movies though, but hey, if I do, it's there.