Grading on an iPad

One of the things that I was excited about trying this summer was doing my grading on the iPad as a tablet. The general pattern that I considered was to have the kids use dropbox to submit work. No problem. Then, by opening the file as a pdf, I can annotate it and send it back through dropbox to the kids. By using handwriting on the ipad, I can grade they way that I've been comfortable (better than using "review" in Word) and go paperless. The system worked great except that the writing program, iAnnotatePDF, did not show handwriting well. The program drops many gestures, like dotting i's and crossing t's. Does anyone know of a better program for this? I came across an app for "Expert PDF" (or something like that) that talks about annotation and it gets great reviews but I don't know about that or something better.