These are the crosshairs I use, I wanted them to be easy to see while blocking as little as possible. For some reason the engine makes them slightly blurry, so I had to add a few things to the autoexec to fix it. Also, you might have to figure out a crosshair size that doesn't mess up the shape.
1024x768 - best crosshair size is 29
1280x768 - size 23
1366x768 - size 22