Should I Get Fallout 3 on PC or Xbox 360?

I'm past the point of deciding whether or not to buy Fallout 3, my problem now is what platform to get it on.

I have a decent gaming PC (it does Crysis on Medium/High without trouble) and an Xbox 360 both of which have their own pros and cons and no matter how much I ponder the question there's never an obvious winner.

Both setups are running 5.1 audio with the Xbox 360 attached to a cheap-ass plasma and the PC using a 4:3 ratio 21" CRT monitor.

PC
Pros

• Finer control with the mouse for aiming and shooting in first person view. That said the game can be played using a non-realtime combat system where this pretty much becomes irrelevant.
• Can play with less chance of the kids walking in during one of those amazing "Crash Mode" death sequences.
• PC edition is $10 cheaper than the Xbox 360 version.
  

Cons

• I only have a 4:3 21" monitor but I am sitting closer to it.
• Moving around in the game is done in the third person (like Oblivion) which sucks dogs balls on a PC.
• No Achievements. :(
  

Xbox 360
Pros

• XBox 360 Achievements! Yes, I'm an Achievement whore...
• Third person movement is much more natural and intuitive with the analog sticks on the controller.

Cons

• Targeting in first person view is far from accurate with a controller but as mentioned above, may not be necessary to play the game.
• Xbox 360 version is $10 more than the PC version.

So which version do you reckon I should get!?!?

For the nerds among us my PC setup is as follows:

Intel Quad Core 6600
4GB RAM
GeForce 8600 GT (needs replacing as it's slowing me down but should run Fallout 3 OK)
64bit Vista Home Premium