1) Personal preference -- I, myself, prefer DSL... it's not a shared network (at least up to the DSLAM) and I've not had any serious problems with it... although a LOT of people swear by cable... really depends on your providers and what they can offer for speed.
2) Wireless is great, however we run both here - wireless is convienent, but with that comes the tradeoff in security. Even with the new technologies such as 802.11g (which supposedly offers a higher level of security than 128bit WEP) - I just wouldn't trust putting my private data over the air (I'm one of those people who is careful not to give my CC out over a non-encypted/non-digital cordless phone too). Depending on your needs, going with a wired network is pretty easy if you either don't mind cables running all over, or can punch holes in the walls. If you still want wireless (I love it for the fact that I have 2 PDAs with 802.11b and 2 laptops with 802.11b so I can roam), just make sure it's on a seperate network segment and you're not broadcasting your FTP and E-mail passwords all over hell and back
There are ways to make wireless more secure, of course... IPSEC on the workstations, or SSH tunneling, etc... but that can be a pain to set up.
Hope this helps,
CGI