Go for the desktop, u cant upgrade the laptop - I had a really nice desktop pc a while back and swapped it for an alienware gaming laptop, really regreted that move, sold a couple of months later and went back to desk, far far better ..
You will feel the same if you buy laptop - you'll regrete it too - honestly
Next year, you can start to upgrade the desk if need be - Laptop? you'll have to sell to get a better 1
Oh, and dont forget monitor size, You'd rather play on a big screen then a small 17"
But this is all just my opinion -