When is the patch more effective for birth control?

Depends. The patch is more effective than condoms and diaphragms. It is as effective as the pill. It is not as effective as the iud.
Easier for some. The failure rate for the patch is fairly similar to that of the pills: ~9% in typical use, and <1% with perfect use. But the patch may be easier for some women to use, as you don't have to remember every day.