I dont want to get to deep into this conversation but as a lender there are some things you should know about your credit cards and credit reports.
1. Never ever use more than 75% of the balance, 50% is better. High trade limits will drop your score.
2. Never cancel your oldest credit card, nor the one with the highest limit. These are your best reporting tools, and high open limits can be a concern but also show someone is willing to lend you that kind of dough.
3. I highly suggest two credit cards for emergency and daily use. One that is paid off monthly, another words your using "their" money temporarily. This is also smart for internet purchases and buyers protection on large items. Second, a low interest (not short term balance special) card for emergencies and balance layovers.
As Tonya offered, debit cards should never be used in rentals (ie. tools, cars etc.) , room rentals, and gas purchases. Each can cause alot of headaches especially for those cutting it close each month. Paying banks NSF/Overdraft fee's is not a wise decision and its getting harder by the day to get them back !