Well, that really depends on which airlines you can see yourself using. I love Jet Blue - but the credit card only earns 2pts/$ on grocery and restaurants and 1 pt/$ elsewhere. Compare that to Chase Ultimate Rewards where you can earn 5pts/$ on quarterly freedom cards and convert those URs to JetBlue at 1:1 ratio. Or Amex Gold Charge Card which earns 4pts/$ on Grocery and Restaurants and converts to JetBlue at a ratio of 1 : 0.8 . (sometimes also 1:1 if they run a JetBlue bonus)
So basically, while I like the JetBlue+ card for the benefits - it is much better to put bonus category spend on other cards and transfer the points to JetBlue.