What is the difference between the WPA2 Personal, WPA and WPA2 WiFi security passcodes?
Both 'WPA' and 'WPA2' use AES to encrypt the information transiting the WiFi network, but 

WPA uses something called TKIP to manage the keys used to encrypt the data. TKIP is vulnerable to attack (it's not secure) and should not be used. 

WPA2 uses AES-CCMP for key management.

"WPA/WPA2 Personal", also called mixed-mode, allows negotiation of key management modes and reduces the security of the network to the lowest common denominator.



BOTTOM LINE: If you're concerned about security/privacy of information on your networks (wired and wireless) , DON'T use WPA or WPA/WPA2. Use WPA2 only. And, if you don't already know, WEP is basically the same as having no security at all.



Another poster points out that the 'Enterprise' modes send authentication requests to a server before allowing a client on the network. The two big advantages are: 


central management: I don't have to set keys on every access point, and I can disable accounts of individual users. There's also traceability: I know which WiFi device belongs to which user.
much longer keys (like 2048 bit, versus 128 for 'personal'). This further decreases the likelihood that an attacker can figure out the key in the time it's in use. 


The 'personal' pre-shared key ("PSK") is derived from the passphrase you type into your client, so even if PSK allowed long keys, you'd have to type a passphrase that most people would object to.