I concur the top button is best, I've also been making buttons using the same pic but a different colour for different states.
I'm having trouble after I set an PNG LED then set an image button with no picture, so in theory it's a transparent button, but after overlaying it with the LED the LED doesn't show up correctly.
I tried to diagnose the problem by moving the transparent button half way off the LED. You can see what happens.
BTW I'm using Screen 4.