Okay, if you are deciding on either ethernet of USB... go for ethernet!
If I am correct, ethernet is independant of the OS your are using, whereas USB is OS dependant. And since you are given a choice to choose, go for Ethernet.
For cable, yes, I must agree it is fast, provided the area you are in do not have a lot of cable user, if not, you will be sharing the bandwidth with them, then, it will be slow. See it as a water-pipe with a lot of outlet, the more outlet, the least water and force it will come out.
Whereas for broadband, it is a dedicated water-pipe to you. No one sharing with you.
But since you already take it up with SingNet, no point thinking about cable lah. All the best for you with your service with SingNet man....
(Someone please correct me if my info is wrong hor.... thank you)