My husband and I are planning our trip to Andaluzia in September and we are not sure if we should stay in Granada 4 nights or just stay longer in Seville.Our plan is Madrid 6 nights with day trips to Segovia and Toledo and 6 nights in Seville with day trip to Cordoba.

You can take one day from Seville and another from Granada and make a two night stop at Ronda, visiting that city and nearby White Towns.
4 nights in Granada, I think it may be much. You could make a daytrip to Alpujarra or even Priego de Cordoba, but that should mean keeping the car all those days, that in Granada (as well as in Seville) is not necessary if you stay in a hotel in the city center. In fact, parking the car may be a problem and a 12 to 15 eur. expense daily.

I agree with Josele that four nights in Granada is probably too many; IMO six nights in Seville is definitely too many.

It would be helpful to know if you are, in fact, traveling by car.

Thank you for the response. We will be traveling by train. We did not want the troubles of a car on this trip. First we thought we should also stay 2 or 3 nights in Barcelona, but finally decided to skip it and leave for another time. We have been in Barcelona 2 years ago and love it so much. But will be another trip I trust.

Not sure why you're giving Cordoba short shrift. I would reduce # of nights in Seville and Granada, spend a couple of days in Cordoba - which is beautiful and fascinating, then do a couple of days in the white towns.

It is possible to do Ronda by bus or train for a day from Granada? How long will take? What do you suggest that we see in Ronda in a day?
Should we take a bus or train from Seville and stay a night and from here go to Granada?
How about Cadiz taken a day trip from Seville?
Just a note: moving from one hotel to another does not appeal to us, we really rather take day trips.

I feel the same way that nytraveler. Cordoba is very interesting, ( El Caballo Rojo is a very nice rest. do not miss it in Cordoba), Sevilla is a city where you can easily spend 5 days, two days in Granada and go to Jerez for the other day. All these cities are easily access by train or bus. Good luck. Sevilla has to be enjoyed little by little you have to get the feeling of the city so I think is a good idea to spend at least 5 days in Seville.