Being British, I would say maths. As it is the shortened form of Mathematics, I would say that maths is more correct (I am now ready to be flamed by all US members). After all you do not say mathematic when refering to the subject.
You'll find all sort of these things when comparing British English to American English. Spellings (neighbour/neighbor, tyre/tire), pronunciations (missile, buoy, route), different words for the same thing (autumn/fall, boot/trunk-as in car), and even same words meaning different things (pants, pavement). It is all the fun of learning English.