For reasons that may be entirely subjective, I think that Miranda IM is the best Messenger out there at the moment. I can’t see myself using Trillian, at least, and I’m not going to ever install 4 different Messengers just because my friends can’t agree on one.
However, there’s one thing that’s really annoying: The installer you can download from the Miranda webpage gives you only half of what you need, and insalling the rest is a pain for Joe Average User. For example, you can’t use it with GTalk because it lacks the OpenSSL libraries required to do that. You can’t use it very well with ICQ, because at the rate that the ICQ servers are going up and down, you need a plugin that automatically reconnects you. And there are no Smileys! And… there’s more, but you get my point.
So yes, I’m really considering bundling the important stuff in my own installer – if only to make it easier for friends to switch ;-P