All 3 are worth visiting,but I would opt for Granada to see the Alhambra,and Cordoba for the Mesquita.
I have driven/drove? to see these 2. The Alhambra has its own parking area the Mesquita doesn't.

I would encourage you to try and get to all three - Seville is a very beautiful city and the Alcazar palace and gardens easily rival the Alhambra any day. Add in the Cathedral and the original cigar factory where the events in the opera Carmen took place and you have another wonderful full day out. Depending on where you are staying I would suggest that you think about taking the train or the excellent express buses - all three cities have pedestrianised the older heart to the city centre and are a nightmare for driving around whilst having the benefit of being really compact and 'walkable' - once you get there you won't really need the car to get around the main sites in all three cities. All have good public transport within them too and whilst the Alhambra is away from the city centre there's an excellent cheap, fixed fare shuttle bus that will take you up the hill to it.

SM

Having done the tour last year I would opt for Seville and Cordoba any time. I found the Alhambra was disappointing/ over hyped.

fwh