Singapore Expats

Which is better? Why?

IMHO, it depends on your requirements

Assuming you are asking because you want to select some choice for your home network.

Ethernet: If you want to stick to your working desk and a computer on top of it then Ethernet is sufficient. (Remember most of the ISP plans does come with a Ethernet port and cable).
So no additional money to be spent on anything. Quite stable connection.

Wireless: You want to use your notebook in Drawing Room, Bed Room, Living room or anywhere around your home. Ofcourse Wireless is required.

You need to invest some more money ( Buy a wireless router or get it from ISP), Connection is not as stable as Ethernet.

I dont want to talk about Security unless you are working for a secret agency ( If you are then I guess you dont need my opinions)

Also, ethernet is faster than wireless (though if it's for internet surfing, it really doesn't matter since you're limited by the broadband speed).

Ethernet: Uses the standard ethernet cable. Secure.

Wireless: Doesn't use cables, but you need to secure it, which can affect performance as there is an encryption overhead unless you use WPA security.