I'm rebuilding credit after the nightmare that was my 20's. My current set-up is pretty simple because my spending is simple and I'm saving higher tier cards for when my finances are exactly where I want them to be.
My wallet currently holds:
Capital One Savor card: 3% on groceries, 4% on dining/entertainment. These are my top 3 spending categories, and CapOne has broad definitions for them. Dining and grocery includes more than it omits. Entertainment works for all of my Bandcamp and vinyl purchases, which is where most of my truly disposable money goes. It also includes bars, movie tickets, concert tickets, museum tickets, tickets to go fruit picking at an orchard... Basically every thing my wife or I does for fun somehow gets caught under the 3%-4%.
Citi Custom Cash: 5% on gas. Between my work commute and all the recreational driving we do, we get damn close to the $500 cap.
Capital One Quicksilver: Anything that's not gasoline or something covered by Savor goes here. Most of my bills, included. There are better flat rate cards out there, I know, but I do all of my checking and savings with Capital One. And with Savor being my most used card otherwise, I like having as much as possible in one place. And their customer service has always been fantastic to me. Simplicity and peace of mind are worth a fraction of a percent.
A few years running, my accrued cash back has paid for most of—if not all of—a very nice night out with my wife for our anniversary. I might be able to stretch my rewards a little further with more effort and cards, but I value simplicity and having a small rotation of cards keeps me far from the nagging "I could get 5% back if I bought this!" thoughts that I tend to get lol. My set-up keeps me honest, and a beautiful night with my wife that's paid for with the money I saved on things I was going to buy anyway is enough for me.