Last week, I began my migration from GyazMail, which I've been using just about as long as I've been using Mac OS X, to Apple's Mail application.
I chose GyazMail for one simple reason: It's a plain text email client, and I'm a firm believer in plain text email - no colors, no bold or italic, no big or small text, no use of multiple and/or unreadable fonts, no VCF cards, no embeded images. Nothing but good old fashioned text (plus attachments for images, MP3s, PDFs, Word documents, etc.). I'd used and loved Claris Emailer in my Classic Mac OS days and also used PowerMail.
How things have changed over the years. I do most of my personal email using Yahoo Mail, and Yahoo does everything in its power to get you to avoid using its simplest, fastest interface. And I get a lot more "enhanced" email these days with photos and the like. I don't tend to send fancy email, but even plain text diehards have to realize that the world has moved on to something much more customizable (for lack of a better word).
On top of that, GyazMail isn't the most stable email client. It works well, and it's been a pleasure to use it, but (1) it doesn't remember which emails you may have had open when you quit it, (2) it randomly quits without warning, and (3) it often reports that it has spontaneously quit when you quit it. Enough annoyances that over time I decided it was time to switch.
I'm not a huge fan of Mail, but it's free, it integrates perfectly with SpamSieve (the best anti-spam tool I've ever used - highly recommended!), and I've been using it for some time with a few email accounts I don't access very often. I've also learned that, unlike GyazMail, it has no problem working with multiple Gmail accounts - and I love my free Gmail accounts!
So last Friday I migrated my account settings one-by-one from GyazMail to OS X Mail. It took some fiddling with outbound server settings, authentication, and the like, but now it's working beautifully with my .mac (MobileMe) address, three Gmail addresses, and 4 different lowendmac.com addresses. And now I can quit my email client and have it re-open messages I had open when I relaunch it.
I'm very happy with the switch.