I wouldn't say there were any particular advantages/disadvantages for these two when compared to each other. In actual fact, what you want to be comparing is the internet and the intranet. Ethernet is more the technology upon which local area networks are based. The adv/disadv really depend on what you want to do. The internet can be thought of as many LANs connected by routers. This has the advantage of shared information. But the disadvantage of decreased security. A Local or Metropolitan area network will most likely have faster transfer rates than a Wide area network due to the close proximity of computers.
internet/ethernet/intranet/sub-ethernet, look them up on goooooogle.
Ethernet is strictly a UTP (nowadays 100Mbs) wire based Local Area Network system, might be connected throught routers/bridges/hubs to other LAN's but remains a strictly local network.
You can't compare these 2... Internet is this huge network full of more or less useful content. Ethernet is just a technology ( wires, routers, protocol, etc. ) that is used to connect computers together, to make all sorts of networks, such as local networks or big ones like the internet.
You are not comparing like for like. As explained, ethernet is a technology used to connect computers together in a network. The internet is more of a concept encapsulating many technologies.