Skype used to be great (this predates the MS switchover). They were the first major messaging network to get the multi-client use case right (i.e. sign in from your home desktop, your work desktop, and your phone at the same time - under skype this will just work).

Sadly the increasingly forced updates always made the UI/UX worse, the phone client was a resource hog, and they weren't quick enough with a user-friendly web client. Meanwhile Slack showed us all how it's done.

I'm genuinely trying to get my friends to switch to AIM - as far as I can tell that's the free option that comes closest to getting it right.