I don't agree with the above chart. If you have $300 in groceries per month, you have $250*0.05% + $50*.01% = $13 in rewards per month, which equates to $156 per year. For the Amex card, you get 6% back on the entire $300 per month, which gives $216 per year. However, you also have a $75 annual fee, which means that you're left with $141 per year. The catch is that you have a lot of variance in your spending, and the results change dramatically depending on how much you spend. If you're close to $300 most months, the math will hold up. If you're oscillating between $500 and $250, we may need to recompute.
Overall, Sallie Mae is probably the better option for your wife. As a perk, you get a 5% gas card and 5% off on Amazon.
