Desktop or laptop? Keep in mind I'll be in the military
For that, getting a laptop is more practical. How much processing power do you want ? Laptops these days come with state of the art CPU's with bad ass 3D capabilities with a sufficient amount of RAM. Laptops can also connect to monitors or HDTV's, you can also plug in a mouse and keyboard, close the laptop and instant desktop. You won't want to haul around a monitor with the tower with cables and other items.
If you're moving around a lot a laptop is obviously better. If you want a gaming system, check out this site for idea on which parts to get. Get a big thumbdrive so you cam move files between them.
if you want to play high end videogames, get a desktop. they will usually last longer than the standard 3 hears because of their upgradability (assuming you dont just get a microtower)
but if youre gonna be military, i highly recommend a laptop for its go anywhere ability, and if you arent intending to play high end videpgames or use programs that require alot of resources (like photoshop) then it should satisfy your needs.