"A Gallup survey conducted in April 2014 found that the average number of credit cards Americans say they carry is at an all-time low. According to the Gallup survey, the average number of cards owned by all Americans -- including those with no credit cards -- is 2.6. Among Americans with credit cards, the average number of cards owned is 3.7. The percentage of Americans who have no credit cards rose to 29 percent in 2014, up from 22 percent in 2008.
Among the other 2014 findings:
33 percent had one to two cards.
18 percent had three to four cards.
9 percent had five to six cards.
7 percent had seven or more cards."
hmm so I guess Myfico members fall somewhere below 7%.
When you want to build credit, you should consider both obtaining only quality cards (those that provide the best cash back for you, or the lowest APR if you carry balances, or the best travel points, whatever is best for you). But, you also need to consider if you want to obtain a lot of cards, in order to add stability to your credit.
You can certainly build a good credit score with just one card. But, years from now when you want or need another card or loan, your Average Age of Accounts will be halved by just adding one more card (or mortgage, or car loan, etc). I currently have 11 open and 3 closed credit cards on my credit reports. If I apply for a new card, it barely dents my AAoA. And there are always good reasons to open another card (better cash back, great sign up bonus, very low APR, etc). So, once you have a few cards with some age to them, are you actually planning to USE your future good credit to benefit you? Will you apply for a morgage, car loans, and additional cards? Do you mind that this will lower your AAoA and thus affect your credit? If so, you need a bunch of cards.
The next thing is, you don't want a bunch of low quality cards. Ideally you want Premium Bankcard Accounts (cards issued by Banks, with $10,000 credit limits or higher). You're not going to start off with those limits, but start building a group of quality cards that benefit you and are mostly issued by banks, and work on geting the credit limits increased with usage over time.
If you're interested in cash back cards, click on a card in my signature, that will take you to a thread that contains a bunch of spreadsheets I created. You should be able to find some good cash back cards in there for the categories you spend in, and the amounts you typically spend.
Dude...everyone knows it's 30! 
My master plan is to have one card from each major network (VISA, MasterCard, AMEX, Discover). I just converted my Citi ThankYou Preferred to the Double Cash which is MasterCard so I've met this goal.
My next step is to have the limits on each of my cards raised up to $25,000. In the middle of June I'll be able to request my next CLI on my AMEX which I hope will give me the $25,000 I want. Once a card hits $25,000 my next step will be to lower the APR on it as much as I can (just for fun... I pay in full). Then I'll be done!
My next step is to have the limits on each of my cards raised up to $25,000. In the middle of June I'll be able to request my next CLI on my AMEX which I hope will give me the $25,000 I want. Once a card hits $25,000 my next step will be to lower the APR on it as much as I can (just for fun... I pay in full). Then I'll be done!