My Citi Double Cash is my default card for everything except groceries, gas, and certain department stores.
For Groceries, gas, and certain department stores (Kohl's, Macy's, and I think JC Penny in my area) I use my Blue Cash Preferred (6% cash back on groceries, 3% cash back on gas and the stores, 1% on everything else).
Based on rotating categories, I will sub in my Chase Freedom for the 5% quarterly specials
For large technology purchases, I will use my Best Buy store card for the cash back in the form of gift certificates.
I also have an AMEX traditional charge card that I use a lot when I go on long business trips because it has no pre-set spending limit though it does have foreign transaction fees which suck.
If my international business travel becomes more consistent than hey can you go to X for 3 months but then changing their minds a week later, I may upgrade my traditional green card to the AMEX Platinum because even though the annual fee is $450, I would be able to get lounge access in many many airports, plus it would reimburse for my Global Entry fee, and I think I may also get some free checked bags (though that is an expensable cost usually).
My default overseas card is my ancient Capital One World card which has crappy cash back but no foreign transaction fees which generally are 2.5% so it's a better deal.
Edited to add: I also have the Target Redcard so 5% off all purchases at Target.