In my opinion the classical selections on all of them suck. iTunes may be the best of the bunch. They have some things from the London and Deutsche Grammophon labels that are quite nice, but they don't have enough breadth to be really attractive to somebody picky enough to want specific things. It's partly demand & demographics, and partly the labels. Some smaller labels (for example Koch and Naxos) have been very aggressive about getting their stuff online. If you're looking for hot current recordings (say Yo-Yo Ma or Hilary Hahn, both of whom are fabulous, don't get me wrong), you're more likely to find them. If you're looking for George Szell conducting the Brahms Symphonies you can get them for about $20 or $25 on 3 CDs. If they were on iTunes they'd probably be $9.99 per disc--why wouldn't you just buy the CDs and rip them? Hell, I paid $2.49--including shipping--for
this. There are just too many excellent budget-priced and used classical CDs available to make downloading make a lot of sense. (Some people would say that's a big reason that new classical recordings of any stripe don't make sense, but that a different argument.)