Depending on what 20-something means, income, bank relationships, spending ability & credit score the answer could recommend something as low level as the Capital One Venture card on up to the CSR but as previously stated the CSR is of value mostly to people that do a certain amount of travel or can put through enough spending for points to justify paying the annual fee.
Even getting a CSP requires decent credit and generally previous credit card use. I'd suggest going with the Chase Freedom with the cashback bonus and then in 6mo-1 year going for the CSP. The cashback bonus is a nice chunk and will pay for the CSP annual fee for the first year, with $50 remaining, while building credit.