Distrokid is a relatively new company, but they were the first company to offer unlimited distribution for a one-time annual fee. It’s a simple platform with no bells or whistles and very easy to upload your music to.
The turnaround time for having your music actually posted to the platforms is great! They charge no commission – you keep 100% of the royalties.
They have a low annual fee for the service, but do have some add-ons when uploading your material.
For example, there is a 'Leave Your Legacy' option add-on. This means that if you die or there is a lapse in payments to Distrokid, they will never remove your music from Spotify, iTunes, etc.
Some of the add-ons are more expensive than the subscription, but you don't have to order them for every track you put up. I'd recommend only using the add-ons for larger albums or compilations so that you're not double dipping on payments so to speak.