The Flex is an excellent beginner card to get and the high rewards rate in the rotating categories are very nice. There is always one area each quarter that is super good, like Amazon or Target. It also gets a really good point multiplier on dining as well. 

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The Unlimited is also an excellent card. It gets a lot of the same point multipliers as the Flex, but one key difference here. Instead of the rotating quarterly categories, it gets a flat 1.5x points on everything not in a point category. Meaning, it's a great catch all card for all miscellaneous purchases. 

My suggestion is to get them early on as it is a Chase credit card and they are stringent if have opened a lot of accounts recently, notably the infamous Chase 5/24 rule, which states they will automatically deny you if you have opened 5 or more personal credit cards in the last 24 months. 

Overall, it is an excellent card and I highly recommend getting this card. There are so many redemption options like straight Cashback or redeeming for travel. Later down the road, you can even pair it with something like the Chase Sapphire Preferred and use Transfer Partners to get even more value out of this card.