When I target a competitive site to reverse engineer I look for sites who have been paying for advertising for more than 3 months consistently. My logic is that if they were able to hang in there paying for traffic for more than 3 months they are producing some profit or enough return on advertising investment to make it worthwhile. These are likely successful campaigns to study.
There are many tools you can use. I actually use a combination of several tools when I do this research. One I can recommend to you is:
SpyFu