Well the prompt for html/plain text can be turned off... But I also had a hard time finding it when I started using Thunderbird. Junk in your inbox - use a e-mail server with a good junk mail filter... your e-mail client won't ever be as good as filtering... and you don't want to be downloading tons of e-mails before you can filter them...

I agree with your other pointers....

But no, I can't recommend another e-mail client