Definitely use a laptop drive. There are a lot of reasons relating to power consumption, voltage, shock tolerance, and heat.
- Laptop hard drives use a LOT less power
- Most laptop drives use 5V, not 12. You'll save money on the PSU.
- Laptop drives are generally rated for >100 G's of operating shock
- Laptop drives run cooler and have better heat dissipation
Note that laptop drives are rated for operation in conditions that head units just aren't. It shouldn't be a problem.
Whatever you mount, you can do it anti-shock anyway. If you're worried about constant vibrations or disturbing shocks, you should try to get a fanless motherboard so you don't have to worry about fans dying. For the Hard Drive, I'd get a 2.5" -> 3.5" adapter or drive rails and use a few layers of double-adhesive weather stripping or somesuch to mount the rails to your enclosure. That should help minimize the vibration coming from the speakers.