Any of them can be made to sound good. However, IMO, Macs are the most natural choice for music. I use a Mac Mini of the series right before this latest release. The caveat with the new mini is you cannot upgrade the RAM. Also, the processors are duo core instead of quad core Intel's.
The MacBook Pro would be my second choice but the IMac is decent too.
I personally use a mini with a quad core I7, 8 GB of RAM and a 516 GB SSD. I also use Pure Music 2 with an outboard drive to store music on. iTunes is strictly a library file using the Apple Remote app with an IPad. Works beautifully, sounds great. Only time things go south is when the home wifi gurgles. Apple's remote comes in handy at those times. You also will need a monitor. Price can dictate which way to go.
The MacBook Pro would be my second choice but the IMac is decent too.
I personally use a mini with a quad core I7, 8 GB of RAM and a 516 GB SSD. I also use Pure Music 2 with an outboard drive to store music on. iTunes is strictly a library file using the Apple Remote app with an IPad. Works beautifully, sounds great. Only time things go south is when the home wifi gurgles. Apple's remote comes in handy at those times. You also will need a monitor. Price can dictate which way to go.