Firewire 400 has better continous data throughput than USB 2, even though the theoretical max is better for USB2. The design of firewire means a firewire chip controls the firewire devices on the bus, not the CPU like USB too. Firewire is definitely superior, it's just that a lot of people don't use it as USB2 will do, and comes on most peripherals.
All the best professional quality soundcards I looked at when I bought one recently (top contenders for me being MOTU, Apogee, and RME), used firewire. Now if you think you might want a Firewire soundcard and/or HDD then get the whitebook and save yourself money at the same time. If you know you'll be fine with a USB soundcard, and you really want a snazzier looking aluminium one then spend the extra.
95% of people can live without firewire, it's only the fact you said you'd be doing music with it that caused a few alarm bells. If they're only small-ish projects and you have no plans of wanting a high quality firewire interface then it's all about paying 30% extra for slightly faster memory, 40GB more HDD (neither of those drive would fit nearly enough for me regardless), and extra shiny aluminium street cred.
In my case I'd have to buy the Whitebook because of my FW MOTU 828mk3, and with the spare money left over I'd buy myself and my fiance a nice meal out, buy some new shoes & clothes, and have a couple of nights down the pub with my mates!