To be honest diet pills are a waste of money. They promise the earth, have great marketing people behind the product, making you believe you will be size zero in two weeks, and because we are desperate and gullible, we fall for it.
That said, I tried Rasberry Ketones last year along with a healthy diet (sort of!) and exercise (20 minutes per day on the treadmill) and did lose weight. I decided it probably wasn't the pills helping at all, so stopped taking them. I still lost weight but in fairness, it was not as much. I started to take them again, and weight loss again increased.
Before that, I tried every pill known to man (more often woman in this case actually!) and none had any effect. Oh, apart from one I tried about ten years ago and is now banned - whoops!
Seriously, your best chance of losing weight is by following a healthy diet (or if you are like me, just cut out chocolate, biscuits, cakes etc), and do at least 20 minutes exercise per day that makes your heart beat faster. Like a fast paced walk, treadmill, aerobics, etc.
You don't need to follow a set diet or invest in workout DVDs, all you need is the will power to stick with it, and believe me that is not easy, especially in the first week or so.
Good luck - you can do this!