Hi Flygirl.

I would echo Dagaetch comment's. I'm in my early 20s but have been at points came since I was 16. So if you are new to this whole thing then I would get the following cards (albeit not at the same time if you are worried about your credit score).

1) Chase Freedom: I love this card for the 5% cash back categories. You can get 5% cash back on up to $1500 worth of purchases (7500 points) in each quarter. The categories change each quarter. Right now they are supermarkets and movie theaters. It's a really easy way to earn points. I believe there are sign up bonuses for 20000 points. It participates in Chase Ultimate Rewards.

2) Chase Sapphire Preferred: This is my default card for pretty much all purchases in Food and Travel and anything foreign. 2% cash back on Dining and Travel and this includes everything from a fast food chain to fancy dinner and cabs to trains and rental cars. The fee is waived for the first year. The best sign up bonus right now is 40000 points. This also participates in Chase Ultimate Rewards. And if you have this card, then you can transfer your points to a variety of airlines and hotel programs. The best thing, is that if you have the Chase Freedom card as well, then the points you earn on that card you can transfer to your Chase Sapphire Preferred and then transfer those points to airlines and hotel programs as well.

3) SPG Amex. This is a good intro card for Amex, especially if you only stay at SPG properties. Then the points will really start to build. For having the card, you get SPG Preferred Plus status, which is basically gold without the possibility of an upgrade. The Cash and Points option is the way to go here. You can easily get 4-7 cents/point using this method, so it's really lucrative. Also, Amex does some great promotions with this card. They recently put on an event at Tribeca Film Festival for people who had this card. $70 for an open bar, food, a movie, and a discussion with the movie's creators. You can transfer the points to a variety of airlines and programs at a 1:1 ratio, and for every 20K points you transfer, you get a 5K bonus. However, I still think the Cash and Points option is the way to go if you stay at SPG properties a lot. You will also get 2 stays and 5 nights toward elite status in case you are aiming for SPG Gold or Platinum.

Happy to shoot you over a referral for the SPG Amex card, just send me a message.