3 days in Madrid and 3 in Barcelona sounds good.  Both cities you can certainly spend more time in, but if you are looking to hit a couple others, 3 in each works.
 
I would recommend Toledo as a daytrip from Madrid (75 minutes or so by train).  It is a very interesting city to walk and learn in and lots of college students study at La Fundacion (I did and loved it).  I recommend hitting Toledo on a weekday to make sure students are around and, therefore, the night will be lively.  Yes… I said lively. 
 
If you are choosing between Sevilla and Granada… do Sevilla.  It is a great city to be a tourist in during the day and the nightlife is better.
 
Alright… I will let others respond.  I may write more later.
 
When you do go, have a rockin’ time!  I love Spain and hope you do, too.
 
Happy Trails,
Rick

Barcelona is a must. Many people are down on Madrid, but it certainly does have nightlife. If you are into the college-age crowd though, I would do this:

3 Barcelona
3 San Sebastian (not a lot to do other than hang on the beach and hit the bars so give or take days as you see fit)
2 Granada
2 Madrid (or just cut Madrid out completely)

Sevilla might have more scenery, but Granada is a college town. Much more going on IMO.

Sevilla and Granada are both nice, you can’t go wrong with either one.

Thanks for the input guys this really helps, I think I am going to spend a night in San Sebastian, 3 in Madrid with a day trip to Toledo, and then 3 in Barcelona and 2 in Granada or maybe Sevilla, but I am leaning more toward Granada because of the college atmosphere.

This will be mine in a few wks
3 days in Barcelona
2 Granada
2 Sevilla (I may drive to Jerez)
3 Madrid
 
Are you planning to take train or fly? San Sebastian is a little out of the way….

Train, I am coming in from South of France so its on the way actually. 

[=“times new roman”]When you are in Barcelona, make a day trip out to Montserat. which is a [/][=“times new roman”]monastery perched on a cliff top. It takes an hour by local train from Barcelona. From the station you take a funicular up to the Monastery. Walk around the Pilgrimage trails, before heading into the Bascillica, make sure you are there for the 1pm blessing, the choir boys even come out and sing. Highly recommend this[/]