To me it depends on how much travel you will be doing in the next 1-2 years. For diversity of Airline transfer options, yes, the Amex SPG is the way to go. This is assuming the business transactions will accept Amex. The 50K Citi American Visa Personal and Biz cards are an easy 100K miles for each of you. You can also both get a Barclays US airways card for 35K with no annual fee first year, then buy a pack of gum, let it sit for a few months and they usually send out "spend more than $750 for 3 consecutive months for extra 15K Miles" email. That's 50K more soon to be AA miles there.

Having said all that, if you aren't going to travel much, or if only domestic, or if don't care about business or first class travel internationally, then getting the 2% Cash back fidelity amex card may be the way to go. You can use the money to buy any ticket you want AND get miles and points back.

Based on your numbers, that's $200/month just from the business spending that can be used for anything. And you can still get credit card bonuses mentioned above for plenty of other miles.

Miles/Points depreciate if not used, so hoarding up tons of SPG points or airline miles when you only travel 1x per year domestic doesn't make sense. That's why look at your travel goals for the next 1-2 years, then start earning points/miles toward that redemption. Then spend the rest on the 2% cash back card.