I use a lot of different things.

1) I currently work for myself as well as a company I founded a decade or so ago. The company has an Exchange Server, and I use Outlook connecting with RPC over HTTP (this allows me to connect the same in and out of the office).
2) I have a standard POP3 account with the website of my self-employed business.
3) Also, about 6 years ago I setup an Exchange Server at home, as part of training myself for certain jobs. I've enjoyed being able to give accounts to wife, kids, a friend or two. Also, I access lots of documents on this server when on the road.
4) I have a Yahoo account I use for lots of web interaction.
5) I have a Google account I don't use much for mail, but it's been useful as an intermediate with my Droid (synchronizing Outlook contacts, calendars).

As far as webmail vs. client, I access Yahoo & Google via web, the other 3 using Outlook. The only time I do webmail for the other accounts is when I'm on someone else's computer.