You must mean Tangier.
Everybody's going to say it's like going to Tijuana and claiming you know Mexico, but it's not necessarily so.
On the other hand, it ain't Fez, Marakech, the mountains, the coast, or the desert, either.
If you have a month in Spain and want to lob off a couple or three days have at it. Otherwise it's too much transit/logistical time (you're probably not going to spend a couple of nights at a Spanish ferry port if you aren't headed to Africa).
If I had two months, I might split the two countries fifty-fifty. With one month, I'd stick to one country or the other.