Bear in mind that not everyone uses an email client that displays formatted text. Viewing your message in B&W instead of lime green on puce is probably an improvement, but seeing (or hearing, braille reading...) text you intended to strike out as plain text is likely to change the sense of your message.
Whatever you use, set it up to use IMAP to communicate with your email provider (actually I didn't mention your email provider - they will almost certainly have a webmail client you can use) rather than POP. This will make it much easier switching around. If you use an email service that stores copies of sent messages on the server (like gmail or the Google Apps service that uses your own domain rather than @gmail.com and used to be free for personal users but is now £35 a year) you can even use a number of different clients simultaneously and always have both received and sent emails in sync.