For simplicity, I just recommend a combination of cards. 

Update Dec 2022:

If you only want to apply 2 cards

Option 1 (no annual fee, please): Bilt for dining 3, travel 2, rent 1, cell phone/car rental/flight delay insurance + Freedom Flex for drug store(VGC) 3 / rotation category(VGC) 5

Option 2 (I want to maximize benefits): AMEX Platinum (one flavor per year) for flight 5/pps/coupon book + AMEX GOLD for grocery(VGC,GC)/dining 4

Non category spending should go with VGC, last option should go with Citi Double Cash (a third card to apply if you don't want to play with VGC)

Order to use cards in different categories (if you have multiple cards and don't know which one to use)

Priority 0 (if the store has gift card): consider buy gift card with >8% cashback/discount

- Restaurant: Freedom* (5)>Prestige (5)>Amex Gold (4)>Discover*>Freedom Flex/CSR/CSP (3)

- Grocery: Freedom*(5)>Citi custom cash (5)>EDP(4.5)>Amex Gold (4)>Discover*

- Gas: Freedom* (5)>Citi custom cash (5)>Discover*>EDP(3)>Premier(3)

- Airline tickets: Amex Plat(5)>Prestige(5)>CSR(3)>Amex Gold(3)>Premier(3)

- Hotel: co-brand cards>CSR(3)>Prestige/Premier(3)

- Other travel: Citi custom cash (5)>CSR(3)>Premier(3)

- Select transit, select streaming services, drugstores, home improvement stores, fitness clubs, live entertainment: Citi custom cash (5)

- Rotation category: Freedom* (5)>Discover*

Priority -1 (if your spending does not fit any category): US bank Altitude Reserve using mobile pay (3)>Citi Double Cash(2)>Freedom unlimited (1.5)>2% cashback cards

Never use: 1x mile or 1% cashback cards

Baseline for non-category spending: Visa Gift Card (4MR-1.1%=5.3%)

* only when that is the rotation category

Citi custom cash limit $500/month in one category only

History:

Update Aug 2021:

Option 1: Chase CSR for point transfer/primary rental car insurance/pps + Freedom Flex for travel/dining/drug store(VGC)/rotation category(VGC)

Option 2: AMEX Platinum (one flavor per year) for travel/pps + AMEX GOLD for grocery(VGC,GC)/dining

Non category spending should go with VGC, last option should go with Citi Double Cash

For all the categories: consider gift card with >8% cashback

Restaurant: Freedom*>Prestige>Amex Gold>Discover*>Freedom Flex/CSR/CSP>Hyatt

Grocery: Freedom*>EDP>Amex Gold>Discover*

Gas: Freedom*>Discover*>EDP(3)>Premier(3)

Airline tickets: Amex Plat(5)>Prestige(5)>CSR(3)>Amex Gold(3)>Premier(3)

Hotel: co-brand cards>CSR(3)>Prestige/Premier(3)

Other travel: CSR(3)>Premier(3)

Last choices: Citi Double Cash(2)>Freedom unlimited (1.5)>2% cashback cards

Do no use: 1x mile or 1% cashback cards

Baseline for non-category: Visa Gift Card (4MR-1.1%=5.3%)

* only when that is the rotation category