Welcome to FT!

Your choice of credit cards is your own personal choice, but some things to consider include the following

Are airline miles important to you?
If so, do you have a preferred airline?
Do you want to fly on 1 airline (ie - CO) or do you want a choice (ie - AX Membership Rewards)?
Are hotel points important to you?
Are AGR (Amtrak) points important to you?
Do you have a favorite store/sports team/college/etc... to affiate with?
Is cash back important to you?
Do you want to pay an annual fee?

You need to answer these, and other questions, to determine "which is best". It may be different for you than it is for me.

Also keep in mind that a program like Membership Rewards and those offered by the likes of Capitol One that "promise use of miles on any airline" are not the same! A program like Membership Rewards allows you to transfer xxxxx miles directly to FFP "A" this year and then transfer xxxxx miles to FFP "B" later. A program like Capitol One (while calling their rewards as "miles") are not "miles" that you can transfer to FFP "E" so you can use them for an upgrade or other award. These programs require you to get a set number of "miles" (usually 25,000), and then the credit card company buys you a coach ticket (usually for under something like $400)! If they can not find a ticket for $398, but there is one for $525, the answer they will give is "There are no seats available"! And you can never use these "miles" for an upgrade or for First Class - unless you can find a Frst Class seat from BOS to SAN for under $400. (Then they might! )