Hi,
It's completely normal to have doubts over which course to do!
Is there something in particular that made you want to do those courses? I would maybe make a list of the reasons why you prefer that that course over the other, and have a look into the jobs you can do after uni with those degrees. I would suggest that if there's a course that you think you'd enjoy the most, then that probably is the best option, as you'll be spending 3 years studying that subject, and your postgrad jobs may be in a similar field, therefore it's quite important that you actually like what your going to be spending a significant amount of time doing.
If you find that you want to switch courses, normally its not too much of a complicated process, as long as there's spaces on the other course still. I know quite a few people who have switched courses while at uni in the few weeks, and they found the swap fine.
I would also recommend that you attend a open day over summer, so that you can have a chat with the lecturer's and you may find yourself naturally more drawn towards one course, after visiting the university again.
Good luck,
Suzan - Student Ambassador