I was on Yaz for about a year because Yasmin was giving me migraines... I had no problems with Yaz, but I did have some breakthrough bleeding after being on it for awhile - of course, I also do the thing where you keep taking the active pills and only have a period once every 3 months or so (my doctor suggested this), and that apparently didn't work so well with Yaz. I chose to switch back to Yasmin, and for some reason, no migraines this time
My doctor has also said not to worry about clots, especially since I don't smoke and my blood pressure is fine~