- Cordoba is definitely a better day trip option from Seville.
- However, if you are next destination from Seville is Madrid, you should go to Granada as a day trip and visit Granada en route Madrid
Why Cordoba over Granada
Cordoba is easier to reach
It takes only 45 minutes to travel between Seville and Cordoba, by the frequent, fast AVE / AVANT trains. Both Seville and well as Cordoba stations are centrally located, and so as a visitor on a day trip you will waste no time in getting to the main attractions of Cordoba.
A day is enough for all of Cordoba
The main attractions of Cordoba are all within a short walk from one another. Starting at the Mezquita, you can carry on to the Alcazar, Roman Bridge, and Jewish quarter. You will be done by the early afternoon and return to Seville well in time to refresh and spend the rest of your evening.
Granada deserves more than a day
You should plan the trip to Granada with at least one full day in Granada.
Just the Alhambra in Granada will take you more than half the day to visit. Then there is the Albaicin quarter where you must spend an evening; there is quite an active nightlife in Granada and it is very unique compared to other cities in the region.
You cannot miss the Mirador San Nicolas. And your Granada trip will be incomplete without The Cathedral, Royal Chapel, and the market area around Plaza Nueva, even if you sacrifice the Sacromonte flamenco shows held in centuries old gypsy caves.
Seville to Granada is a long trip
Just getting to Granada is a 3 hour journey whether you drive or take public transport. So you are talking about being on the road for 7 hours - that will not leave you with much time to see anything except the Alhambra. And by the time you return you will be very tired.