Which credit cards are the best?

For years my wife and I have both had our own credit cards. I carry a Visa and an American Express and Janet carries a Diners and a Mastercard. We have always managed fine and there have never been any problems. We were out at friends for coffee the other evening and we listened to a conversation about all the different kinds of credit cards that are available. I made a list of these credit cards. Here it is:
o • Low Interest Credit Cards
o • Instant Approval Cards
o • Bad Credit Credit Cards
o • Rewards Credit Cards
o • Cash Back Credit Cards
o • Student Credit Cards
o • Business Credit Cards
o • Balance Transfer Cards
o • Hotel/Airline Credit Cards
o • Prepaid Credit Cards

So of course we are now thinking that we can improve our situation and save money at the same time by switching to different cards. The big question is where to begin and how to choose our new credit cards. I’ve been looking at credit cards on the internet for 2 days and at this point in time I am no wiser. But I’m learning a lot about the subject.