I'd consider 2 bases. This is kind of hard to answer as you don't mention how much time you have.
I personally wouldn't do a daytrip to visit Sevilla - there's too much to see. Granada can be done in a day but it would be rushed to see much other than the Alhambra. I'd consider spending at least 4 days in Sevilla and daytrip to cordoba (if your time is limited Cordoba can be done as a daytrip but it's gateway for a couple of nights). You could then move east for the Granada and Nerja visits. Malaga would be one base where you could daytrip to each. Or you could stay in Granada or Nerja and visit the other.
Read the Driving Guide for Foreigners. Hotels charge 11 euros a night for parking and there is no free parking in cities.
For train travel, read Buying Renfe Tickets Online.
Thanks, your right my post could have been more helpful, new to the site.
We have about a week to eight days. In past we have rented houses for a week or two in the country side in provence and tuscany and then used that as a base for visiting more major places and found it an enjoyable way to travel. Didn't know if the Andalucia area leant it self to this sort of travel in terms of road quality, distances between things and availability of properties like that somewhere in the "middle" of the various places.
Thanks again and in advance for any thoughts you might have.
When are you planning to visit Andalucia???
andalusia is too big for a sigle base. Seville would be one base, giving you access to Cordoba, and either granada or malaga another base, giving you access to nerja.
I wouldn't rent a car as it's a hassle inside city centers, and public transport (train/bus) is great.
Be aware that much of the Andalucian plateau will probably be like a furnace in Mid-June.
It is quite possible that temperatures may reach 40ºC in mid-afternoon. Seville can be an absolute scorcher at that time. Everything will close down apart from the big stores between 13:00 and 17:00..
If I were you I would recommend four days based in or around Sevilla and four days based around Granada/Jaen.
After much research including consultation with this forum we will be spending 4 nights Seville, 3 nights Granada and 3 nights Malaga. We are renting a vehicle the last day in Seville and will do various days trips from those centers. The journey between points are day trips also.
Thanks by the way to those people who have been so helpful.Edited: 10:37 am, January 16, 2013
I'd consider adding a day to Sevilla and you'll have time for an additional daytrip -Oosuna, Carmona, Ecija, Jerez, Cadiz or Sanlucar. All are easy using public transportation. I prefer this area of Andalucia to the eastern area. With your current 4 nights for Sevilla a daytrip to Cordoba is a must.