Pros of Live Messenger:
1) Signing in is faster
2) Allows you to search contacts, instead of looking through tons
of email addresses or nicks one by one
3) Sharing of files is simpler now, though I disabled it due to
security reasons.
4) When adding new contacts, allows you to move them straight to a
group, instead of creating, then dragging them to the desired group
you want in 7.5
5) You can update contact's information easily
6) You can send offline messages to a contact, even if he/she has
no Live Messenger
Cons of Live Messenger:
1) Nice interface = more lag
2) Sometimes sign out = never sign out
3) Sharing of folders = more security risks
Pros of MSN Messenger 7.5
1) Is a stable release, won't crash too often
2) Simpler interface, so it's not that laggy
Cons of MSN Messenger 7.5
1) As usual, a lot of viruses, trojans and worms target them, and
hard to remove kind.
2) Add contacts first, move them to the groups you want later.
Irritating feature improved in Live Messenger.