For me, MSN was the best at the time, and imo is still the best (msn escargot I mean).
What I liked about MSN (And MSN+ features) were the following:
- changeable displayname
- changeable avatar
- avatars were of decent size
- statusbar/"what are you listening to" etc
- customizeable pretty much everything. backdrops of convos, the UI, fonts/color, etc. You could personalize pretty much everything in some way, even if a bit limited.
- dont think file sharing was limited? i remember sending like 700mb movies to friends over MSN (was easier and faster when we were locally connected etc). The file wasnt on a server, I guess, it just went from P2P, which is why I guess they could do that.
- chat logs were saved if you wanted.
- the program was pretty unintrusive (discord for example is big and clunky, MSN you can make pretty tiny if you wish.)
- The drawing function they added. We had a lot of fun with that, drawing to each other in the chat.
- You could add tons and tons of custom smileys
- It also had a browser version for when you just needed to hop on, on a random PC and not install anything.
- The UI was in "separate" windows. So you could choose which chatting window was big, smaller etc if you wanted, and your main hub/ui wasn't attached to the chatting windows, like how Discord is.
What I wish MSN would have added:
- Changeable avatar and display-name between users (as in, I want Sally to see my ~emo nick~ and Peter to see my xXxedgyxXx nick)
- Group chats that are not temporary (I believe later versions of MSN actually had that, but it wasn't the norm most of its heyday I believe.)
- More "skins" - although I appreciate the "frutiger aero" look of later MSN, I wasn't too fond it it being so forced. Any sort of darker theme on it would get this ghostly sheen over it and any black color was often just a bright grey.
- Saving logs in a comprehendable way. The XML logs of MSN are not the best.