Earning cash-back, points, or even miles all have their advantages.
Cash-back is most liquid, of course, but points can often yield greater value when redeemed for travel or transferred to airline or hotel partners.
Airline miles earned on a rewards card may be the least flexible rewards when they can only be redeemed for flights on the specific airline or partner airlines.
The best rewards-earning choice will depend on how you want to redeem your rewards. Points are generally better when redeemed for travel.
Cash-back can be a good choice when it is allowed to accumulate in your account and be redeemed for a specific purpose in a lump sum.