Personally, I have found spells to be much more affective than prayer. Which in my opinion are almost the same thing. The difference being that with prayer you are relying on some greater being to grant your wish instead of using the "powers" god created within yourself.
More often than not, with prayer, you are counting on god to reverse the results of your behavior, knowing you do not deserve it. It is this spiritual uncertainty that corrupts the spiritual energy you project when you are trying to receive a blessing. When the prayer is unanswered most people tell themselves it just isn't the time to receive the blessing or that it wasn't god's will for them.
For instance a smoker who prays to be healed of lung cancer is actually asking for the consequences of their physical action to be reversed by their god for no real reason. Because they know they don't deserve the divine intercession their faith will not support healing energy.
In my opinion spells are more honest. When you cast a spell, you are literally telling the universe you want something and that you are willing to pay the price to get it. This is why you have to be very thoughtful and precise with what you say when casting a spell. Your spell will most likely get you what you want, however, the side effects or the process of getting your wish can be very energetically costly or unpleasant. Never hex or curse anyone. Hexes bounce back.
You reap what you sow.
You reap what you sow.