Thunderbird is pretty bad.
Side note: I use mutt with gmail imap and have no problem whatsoever. http://wiki.linuxwall.info/doku.php/en:ressources:astuces:mu...
Composing HTML emails need to be disabled for every account. Never had a problem with it.
In the end, mutt vs. Thunderbird is pretty much like vim vs. gedit. gedit is far easier to use out of the box, but vim allows you to define your own (complex) commands, allowing you to basically make your own editor.
E.g. I like GMail shortcuts, so I added macros like the following to my muttrc[1]:
macro index,pager gl "<change-vfolder>?/"
macro index,pager gi "<change-vfolder>inbox<enter>" "go to the inbox"
macro index,pager ga "<change-vfolder>archive<enter>" "go to the archive"
For instance, gl immediately gives me a list of vfolders and does the keystrokes to start a search. So, like GMail, I can immediately start typing a name of a folder.[1] Note: I use mutt-kz
- install Nostalgy addon
- press "g"
- type/select folder name
- profit$
Try the Nostalgy add-on.
But just using mutt is giving up much usability and features with little benefit in security. They're better off using good config and sandboxing with a client that gets more audits and bug fixes.
/s :)
For me, the advantages are: works all over (e.g., i can find out my buddy's apartment address from an email in 2008 even if i'm nowhere near wifi), it's snappy, keyboard-driven (like, really -- Google Mail with their cute mnemonics or Thunderbird with shortcuts don't count), text-only (because i'm a nerd, and perhaps you could argue vague hand-wavey security stuff here), and because i can Elisp my way out of sticky situations. Especially the Elisp.
On that last point, you might well contend that if i used an email client to your liking i wouldn't need to Elisp my way out of anything, but i think that's beside the point. For the first time in years (i've been using mu4e for a year now, and before that mutt, starting 2006) i've actually been able to make my client do exactly what i want using a real programming language -- certain formatting hacks, PGP to certain people in certain circumstances, email address completion the way i want it, etc.
But anyway, it's probably not for everyone :). There's also no such thing as a "best" email client, probably -- i'm just partial to the create-your-own-MUA kit that i've found in mu4e :).
This is waaaay off-topic though, i'm not even talking about mutt any more. Sorry, i got a little carried away :).