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Browse credit cards from a variety of issuers to see if there's a better card for you.
You aren't addicted, you are only getting started, and have some good cards to show for it.
Discover: Check on your on-line account. You get a free, accurate TransUnion FICO credit score every month. Please report back here what that is on your last statement. As noted, you are getting 2% overall with this card, which matches the Citi Double Cash, so use the Discover in place of the Double Cash. Check for the credit line increases also.
AMEX Blue Cash: This gives you 3% on groceries, 2% on gas and department stores, so for those categories it is better than Double Cash. Search MyFICO for the AMEX 3X CLI thread, because after 61 days or more, you can request a CLI to start growing the card. Also check for threads about reducing the APR on the card, that is also very easy to do.
Your Quicksilver cards, as noted, give 1.5% cashback immediately, almost as much as the Double Cash. Quicksliver also has no foreign transaction fees, so if you go to Canada or some other country outside the US, use the Quicksilver to avoid a typical 3% FTF. DoubleCash has the 3% FTF, which often is not an issue, but can be. Check for the credit line increases.
You can go to the Citi website to check their card prequalification page. But you should only apply for the DoubleCash there if you get the lowest APR offered, 12.99% and do not apply if you see a range from 12.99% to 22.99%. By waiting for the 12.99% single rate to show, you will be spending quality time with the other three quality cards you already have, which are as good and in some cases better than the Double Cash.
You aren't addicted, you just don't know what you don't know. So stop apping, and read here more often to learn more before you app for any more cards. And realize, the three cards you already have will take care of all your credit needs for at least a year. So if you get the urge to app, just read more about the three cards you have, and see that they probably beat whatever you are hearing about. Seriously.
I would wait a year and after you have a year and a half to two years of credit history and no more hard pulls apply for Citibank Thank You Premier. Using CreditCardTuneUps calculator they have the best cash back for me. Close to $1500 a year. Though from the forums seems like you need a decent length of credit history, around lower 700 EX/EQ and very few hard inquiries on your file.
So if your setting a goal use the CC Tune Up calculator and see what you should be aiming for. Then garden like nobody's business for a year.
Here is some advice to avoid 'junk cards' in the future.
Just sit down one day and calculate monthly expenses through your bank and/or credit card statements.
Highlight what you spend your money on the most and then find out which cards offer the best cashback or point bonuses.
I know it sounds pretty obvious, but you'd be surprised at how many people really need to do this.