If you are unsure of what field of computing you are interested in just yet, computer science is the best way to start off. In first year computer science, computer engineering, and software engineering do almost exactly the same subjects. If after first year you start to feel strongly towards one of the other computing degrees, you can always use the abundance of electives in computer science to mimick the program you want to get into to make it easier if you wanted to transfer.
Of course, there isn't any need to transfer at all if you like computer science. Personally I enjoy it quite abit because theres alot more choice in subjects than the other two computing degrees.
As a general guide:
Computer science: comp + maths + free electives
Software eng: comp + maths + management (info sys)
Computer eng: comp + maths + physics + electrical engineering
Of course, there are electives in seng and comp eng as well, but not as much.