You've probably decided by now, but:
Speak to both teachers - they know you and your abilities and therefore should know how you will cope with their courses.
Try doing both just for this term. If you find it hard, just try to keep up and put in a little extra time. Any time lost this term is easily found during your 6 (or so) week break.
After this term, make your decision. Further discussion with teachers will help. Preview the upcoming topics, maybe talk to more people who did it and then make your decision.
If that term wasn't too hard then just think: you're a quarter of the way through. If your aren't going great, yet are happy with where you are and the time you are spending then keep it cause it's great support for the 3u and the scaling goes through the roof (6/8 questions =~90% (no i'm not stupid, its the scaling))
But remember, the main thing is the chit chat with the teacher people, cause they have prob seen it all before.
(ps. if i repeated anything anyone else said, it's cause i got bored halfway through reading comments and just skipped to the end. no repetition intended)