Q: What is the best diet to follow?
A: NONE! Diets plain suck, man. They are temporary and shitty. If you want to eat healthy it is pretty simple; consult a food guide and eat your recommended dosage of each food group (more or less depending on what you are trying to do with your weight) while avoiding excessive consumption of oily foods and refined sugars. You can create your own food plan quite easily. IMPORTANT: Once you have balanced your eating and found out what your body requires, THEN you can consider restrictive eating programs if you so wish.
I thought I'd contribute my own view on this issue.
There are situations where a temporary diet is appropriate. However, any such diet should have two properties: they should be sustainable (which keeps them relatively healthy) and they should be carefully designed for achieving the desired goal in a healthy manner. Most diets, including all of the fad diets, are intended to achieve the goal as quick as possible, which means that health tends to get thrown out, as does sustainability.
My own approach, if the goal is reduction of body fat with minimal impact on muscle, is what I consider to be the simplest and most effective rule of thumb possible... and it's this:
Don't eat empty carbs (much)
Now, you're probably wondering what I mean by "empty carbs". It's simple - don't eat a food classified as a "carb" unless it provides other health benefits along with it. Most fruits have a lot of other vitamins, minerals, etc, that make them great, despite being "carbs". Most vegetables are even better... but stay away from regular potato, it's pretty much nothing but starch. If you want something similar to potato, go with sweet potato (despite the name, it's closer to carrot, and has a lot of benefits similar to those of carrot).
Note that fruit juices are a judgment call, but I'd probably put them in the "empty carbs" category. The fiber is probably the most important part of the fruit, and that gets lost when you juice it.
Other things to keep away from are sugars/lollies/candies, any kind of sweetened water (there is a possible exception, here, for natural, non-caloric sweeteners, like stevia), and a lot of the grains - wheat especially. Rice is a judgment call (personally, when I'm holding myself strictly to this approach, I avoid white rice, but permit wholegrain rice). Some grains, like oats, come with extra benefits (but try to stick with wholegrains, anyway).
Oh, and alcohols are carbs, too. But then, if you want to be fit, I suggest you don't drink (there are a lot of things about alcohol that are counterproductive if you want to be fit). I'm a teetotaller, myself.
Obviously, don't drown your food in oils and fats, but there's nothing wrong with naturally fatty foods - especially things like nuts and meats. Dietary fats are essential to your body, especially for guys (it's a key ingredient for your body's production of testosterone - especially dietary cholesterol... just don't overdo it). Egg yolk is the most nutritional part of egg, and egg white alone has components that can be detrimental to your health unless you eat some yolk with it.
And of course, protein is generally good.
If you're going to go very strict with this approach to eating, then you should allow yourself one "cheat" per week - not only does it allow you to eat one of those foods you like, but aren't permitted, but it also keeps your body from adapting completely. But you only need to go this far if you're aiming for something more than just "healthy maintenance". If you are just wanting to be healthy, and have no specific target in mind, just use the above as a general rule of thumb, allowing yourself a bit of empty carb as needed - just don't have too much.
"Too much", of course, is something you need to judge for yourself, but a good way to think of it is like this - only have potato a couple of times a week, and don't have a lot of it on your plate. Don't refuse dessert when you're out with friends, but keep it small. If you have a deep craving for, say, some ice cream, let yourself have a bit. But not a large amount. And if you splurge once in a while, and have a large amount of empty carbs at one point - don't punish yourself too much, but rededicate yourself for a little while, and eat a bit cleaner for the next week or so to compensate.
For instance, I had some family up that normally live quite a distance away, because of a wedding. The night prior to the wedding, my immediate family had these people around for dinner, and there was dessert. I decided to partake. And I also had dessert at the wedding, of course. So my next week is going to be kept strict.
When I last followed this approach strictly, I managed to lose about 4 kg in 4 weeks (which is right around the optimal healthy rate of fat loss), with no apparent loss of muscle, and lost another 4 kg in the next 8 weeks or so after that, again without any apparent loss of muscle. I got very close to my goal. I've since ignored it, and gradually put on weight (although I think I've gained a fair bit of muscle along the way).
One more thing. If you're going to change your diet, it's best to do it in a more gradual way. Want to follow my above suggestions strictly? Give yourself a few weeks lead-in, where you gradually cut back. Sudden changes to diet can cause your body to react as though it's going into a famine - it'll start saving up fat, slowing your metabolism, and will thus be counterproductive. And it'll eat into your willpower as you feel hungrier, and then when you stop following the 'diet', you'll return to your normal eating pattern, but with a slower metabolism, and things will get worse. This is the reason for "yo-yo dieting" occurring the way that it does, and why people who go through it generally get gradually larger/heavier with each cycle.
For those who are curious, I currently weigh about 88 kg. Last time I went strict with my diet, I started at about 82 kg, and worked my way down to somewhere around 74 kg, and I was getting close to the point where abs would start to show. I'm thinking that abs will show somewhere around 78 kg now, due to muscle gains along the way. If people are interested, I'll keep them updated.