What "fuzz" is this referring to? I have for a long time preferred GIMP to paint.net for its portability and versatility, but neither of these compete with MSPaint in any way-- they fill a completely different role.
As I noted elsewhere on this page, Kolourpaint4 is the Linux equivalent of MS Paint. There are others which aim for the same niche, one called (MTPaint? or similar?) for example, but I found them harder to use.
What? Photos are bitmap graphics and Gimp has nothing to do with vector graphics. You're really confusing a lot.
To draw a straight line in Gimp you just hold shift.