Positive opk - clearblue vs fr?

For the last few days I've had negative opk's, but today I took a clearblue digital test and got a smiley face!
But then about 3 hours later I took a first response test to get a more specific idea, and it looks like it's not positive...
Has anyone had any any experience with these two brands? Is clearblue more sensitive? Or did I miss the window? Any ideas?