Great decision!! $20 and you gain the better part of a day!!
We were there in June so I really have no idea what the area is like during the winter, but I really liked the Málaga area. It had a more rural type atmosphere. Remember that I was with kids, so the late night party scene was not high on my list. My daughter did go out a couple times with older students at our school and each time had a wonderful time. There were things to do, but it certainly lacked the hustle and bustle of the other cities!!
My daughter went out in Madrid with the brother of a friend and she was shocked by the endless number of areas of quality clubs and bars.
She felt it would take a life time to explore them all!! It was quite and experience for a her!!! Certainly not one that she could have done in the US!!!! Corruption of a minor at its finest!
Since my other child was only 12, we did NOT join the party. Besides, it all started after my bedtime!!!
They are such different areas that it is hard to help you with your decision. I would guess that Madrid will be wild with adventure for New Years , but will also offer queter opportunities if you can find them. Maálaga will probably be more sedate but very pleasant. Tough choice!!
I love the ocean even when I have to wear a jacket!! That would be the selling point for me!!!