As an artist and as a purchaser of other artists music I find Bandcamp excellent.
As an artist you only have to upload your file(s) once, wav or flac depending on the size, Bandcamp does the conversion for you, when the buyer chooses the format they want. You can upload artwork and bonus items, etc, and you can even sell physical stuff from there as well, and you can set your own prices. All in all pretty damn good!
As a purchaser, everything has been smooth, you choose the format you want, one price regardless of file type, files arrive with no problems at all.
You can listen to whole albums if you want, before you decide to buy or not, very important if you're out there discovering new artists, gives you a safety net so to speak.
I like the collections thing too, it is very interesting having a look at what other people who have some similar tastes, are listening to in addition to those you have in common.
I did sell one of my albums on Musiczeit, but took it off after a couple of months and put everything on Bandcamp, Musiczeit wasn't for me, I have not tried CD Baby for selling, but to be honest I am more than happy with Bandcamp and wouldn't bother looking to sell on CD Baby.
I have bought music from CD Baby before MP3 only at that time, I believe now they offer flac also but I think there is a price difference, although I may be wrong on that. Bandcamp would always be my first port of call for digital, and if I didn't need to go anywhere else then I wouldn't.
I hope this has been helpful.