I'd prefer a detailed one, showing just what TPT is capable of.
Something that's big, and flashy. Like... Dwotci's Desert City 5 or 6.
First, I think icon should be 32x32 (most common are 16x16 for program window and 32x32 for executable). Even with 64x64 (I'm not sure which icon sizes are used by default in Vista/Seven, I think it's still 32x32) it will be quite hard to pack such large image into such small sized box.
Second, I don't think that basing icon on someone's save is very good idea. Just because it's exactly supposed to show what's TPT is capable of, not to show what's can be created in it.
I like idea with using stickman on icon. For me, he's like a symbol of TPT. I mean, he looks quite unique and memorable. But icon shouldn't contain anything photoshopped/gimped.