EU citizens can apply for the Permanent EU Registration Certificate. Family members of EU citizens, however, have to apply for the Permanent Residence Card.
The advantage of the permanent residence is that you can leave Spain for more than 6 months and less than two years without losing your residency in Spain. Also, you will not have to accredit any reasons to remain in Spain anymore (economic means, insurance, employment, etc.).
If you have further questions or you need help getting your spanish residency, contact us here and our lawyers will start working on your case very fast.