What should I buy, a laptop or a desktop?

I'm running on an old Toshiba laptop and it's time for me to buy a new computer. I need something… Mostly for video and music editing, and on my free time, some minecraft. I'm only 14, and I really want a macbook but, I don't see that coming anytime soon.

Here's the reason why I'm stuck in between these two: the desktop is great because it is more powerful, and bigger monitors. But I want a laptop because the ability to use it anywhere would be nice, and it's probably nicer.
My budget stops at around 800-900, because I have 200 dollars right now, and I'm selling my PS3 for another 200, and my step dad will help me out. I'm, leaning on the side of getting a macbook air which is 948. It just doesn't have retina, but I don't think that's a problem for me.

So should I go for the macbook, or settle for a pc. If pc, laptop or desktop?

Added (1). I've seen macbook pro's for 600 on ebay so maybe I'll save up for that, but which should I get

I think you should get an alienware laptop. They are good and prices run from $500 to $1000.

It somewhat depends on what you'll use on the computer.

For example, if you're a hardcore gamer, I'd probably suggest a desktop. Probably Windows as more gaming software is compatible with the Windows operating system.

If you do a lot of admin work, a laptop may be a better option due to ease of access, portability and lighter weight. Again, I would sway more to Windows as the majority of operating systems in admin are Windows.

If you were a designer, like me, (ironically) I'd suggest OS X (Apple). Probably a desktop for higher resolution etc. Adobe tends to be more user-friendly on a mac.

So it depends on what you'll be using it for. Look around, get a vibe for what would suit you. Are you more into functionality or design? Another important factor to consider!

Desktop. Definitely.
Why do I recommend a desktop? I will give you pros of a desktop and cons of a desktop.
Pros:
Faster
Cheaper
Better price to performance ratio.
Easier to upgrade
Bigger screen
Desktops run programs MUCH better such as video editing and gaming. But that depends.
Lasts longer
Cons:
Less mobile
Please don't get a macbook. Macs are very overpriced and under powered. Apple products may seem appealing, but they are not good if you know about a thing or two computers. So don't get a macbook. Just don't.
Because you are using it for gaming and music/video editing you will need a semi powerful one.
Here is what to look for when buying a computer:
Ram. Make sure you have 8+ GB. It helps a lot for video editing and music editing
Graphics power. Better graphics = better gaming. Get it with a GTX 750+ or 650+, or Radeon 7750+. Don't get fooled by video card memory. 1GB is fine, 2+ GB is a waste.
Storage. 1TB(1,000GB) +
CPU power. Intel 4000 series(haswell) is the best. I recommend an i5 or i7. Or for AMD, get an FX series CPU.

You can buy a real good new PC laptop for under $600. Save your money by NOT buy a Mac. Its a premium/luxury brand and they charge you for it.
Just be sure to get one with an advanced graphics card if you'll be doing some serious video editing. If its just for fun then a basic one might do. Atleast 8 if not 16GB of RAM.
The mobility you get with a laptop is great.

If I were you I would not get a macbook. I don't like them at all.