I have 2 paid accounts:
fastmail (enhanced) and GMX (pro)
GMX I mainly use for voicemail and SMS notifications. All fastmail email that meet certain criteria (an is very very probably not spam or a newsletter) is forwarded there so that I can have the email read to me on the phone. Nice thing is, it detects the language (german or english) automatically and reads the email to me in the right language.
Also, all incoming voice messages (I use it as the voicemail for my cell phone) get saved as a .wav file there. A notification is also sent to my fastmail account so I know even with my cell phone off, that I have a message.
GMX (pro, 2.99 a month) features: Unified messaging (only for main inbox though), 100MB, IMAP is available since a few months, they also have spam assassin, they have auto purging folders, pretty powerful but gui only filters, a notification feauture that rocks, HTML composition if needed. For an additional 2 Euros a month, you also get file storage.
Why my fastmail account is still my primary account:
* 100 MB is maximum at GMX, I need more already, and will need about 5%-10% more storage space per year,
* The great user interface which rivals any email program (it is just so powerful)
* The Fastmail team
* Sieve
* SOAP support (just in case I do want to code something cool for my email)
*EDIT* - you get 250MB at GMX - learnt something new
