For a desktop computer, I build my own. You can get a lot more capability for much less money, and pick the components you need or are most important for what YOU want to do with it. The name brand machines are overpriced, and I've found that customer support quality is, um, 'uneven' at best.
Of course, I'm an engineer (Among other things...), so designing and building my own from off-the shelf components isn't a big deal.

Many people new to building their own might start with a "bare bones" kit from a supplier such as Tiger Direct or NewEgg, and add the remaining components they want. You can also easily upgrade individual components later if you find that you need to.
In some areas you may even be able to find classes being taught on building PCs, so you get the help you need as well as a custom machine.
Working a lot with photos and video, I'd recommend going with a faster multi-core processor, lots of main memory, and a separate video card (Not video built-onto the motherboard!), with as much memory as you can afford if you're wanting to run two monitors at high resolution. Also, use a 64-bit operating system rather than 32-bit, otherwise you're limited on how much main memory you can actually use.
I also use a second internal hard drive and an external networked drive for video and photo storage, so as not to clutter up the C: drive. Traditional 'spinning' hard drives are fine for storage, but some people are going to solid-state drives for the main C: drive for the speed.