Yahoo is good, but it's a little too AJAXified for my taste. GMail is a little more subtle in their AJAX.
Hotmail really isn't that bad. It went through a drastic redesign, and it's going to have some sweet new features, like a search sidebar and other awesomeness. I'm having no problems with it for FF3 either. Yahoo mail is painfully slow. Way too much AJAX. Gmail is perfect combination. Just needs multiple file selection and drag and drop.
Hotmail deleted my account and I cant reactivate it so I agree they suck. I had emails in there. I just hadnt checked in a long time.
Another vote from me for Gmail. I did have a mail account with Yahoo, but the spam filtering was useless. Tried Hotmail, but didn't get on with it. Finally tried Googlemail and haven't looked back since.
Hotmail also sucks because of its spam filter, and the fact that you have to make a long and hard procedure in order to be able to send emails to Hotmail if you have a dedicated server.
There will always be issues with hosted free email services - I agree with many above ... my primary gripe with using the web interface to Hotmail is that it is getting more and more bloated with every attempt by Microsoft to revive it (MSN, Hotmail, Windows Live Mail) and forgetting that the primary function is to offer us functional access to my mail. That being said, I get relatively little spam in my hotmail accounts. My important accounts, and those of our clients, are *always* hosted on dedicated email servers that we run ourselves. Ever lose a batch of emails on a free email service (such as MSN, Yahoo! Mail, Gmail, etc.) and try to get a restore done from their backups? Good luck... Rob