I'm pretty sure that it would be your aunt, as she is a degree closer to you than your cousins. The basic idea in this sort of situation (when no kids, spouse, parents or grandparents alive) is to draw your family tree- whoever you get to in the least amount of steps is likely your next of kin for intestate purposes. I don't believe that the fact that she is your aunt by marriage and not blood counts, unless she divorced from your uncle before his death (which is not the case here).
Make sure you keep your will up to date- always important, especially because you're young.
And remember your dear friend kddani when making that will!
j/k