There isn't really a concise answer, wep can easily be cracked and sniffed, wpa will only be possible to sniff if you have the key, to crack the key, you have to run the captured handshake against a dictionary, which depending on your password can be quite easy or very hard/impossible to get.
To better protect yourself use a wpa key with 10+ characters, and mix numbers, letters and special char... In example..
Hope this helps, cheers!!34ckTrac<!4