The Apple Time Capsule hardware device is primarily designed as a backup target for OS X Time Machine backups. It can somewhat function as a NAS storage device like the Apollo Promise, but it is very slow and nowhere near as full featured for file sharing as a NAS like the Apollo. The Time Capsule is an Apple Supported device for Time Machine Backups, and good for that purpose, but it a lousy NAS device IMO.
If your main usage is for file/photo sharing/access, the NAS is a far better solution.