I have a laptop already, but it's a clunky Core2Duo laptop. Still functional though. I also have a desktop too, but that's an even older Pentium D, but also still functional. Plus, I have an Android tablet.
I'm looking to replace either my laptop or my desktop as my main computer. If I get a new laptop, then I'll probably be getting rid of both my old desktop and laptop and have some sort of docking solution when I want to use my laptop on a desk. If I get a new desktop, I could get rid of my old desktop and use my old laptop for portable stuff.
Laptop won't be as powerful (it CAN be, but it'll cost more) but it's more portable and versatile.
Desktop will be more powerful and customizable/upgradeable, but obviously not as portable.