Creatine. I've done it. Gained a good amount of wait on it. The biggest thing is commitment when you're doing creatine. It will not make you cut. It will make you stronger/bigger though.
I gained right away, but my body doesn't respond well to creatine. Everyone's responds well. You won't tone up with creatine. What it does is fills your muscle cells with atp, making you bulkier and having a longer muscle endurance in workouts, so you can lift longer and harder, thus making more muscle, but like I said earlier. You have to be committed.
I know a few people that got fat when on creatine because they ate wayyyy too much. Remember rule of thumb is 1g of protein/1lb of body weight to maintain your weight. To gain muscle you have to eat more then 1g/1lb. But with creatine, make sure you do it right and lift hard and take some simple carbohydrates with the stuff otherwise your stomach will hate you.
Remember. ALl bodies respond differently. I had friends that would load and be on it for two weeks and their maxes would jump like 30 lbs, I didn't have these awesome results, mine went up like 30 over the entire cycle. Good gain, but it was lost once I stopped using creatine. Only reason is, I get a ton of creatine in my diet. I eat one vitamin a day. I call it a steak.