The healthiest diet is the one that you can afford, you enjoy and works for your dietary needs because that's the only one you'll stick to!
I've tried them all, high fiber, high fat, low fat, low carb, vegetarian, vegan, gluten-free, egg-free, dairy-free, refined sugar-free etc. The one that works for me is Primal, which is like Paleo but includes grass-fed dairy. I find Paleo, Keto and Low-carb to also be excellent diets for almost anyone. That said, I meant it when I said the best diet is the one that works for you. Some people can't stand meat, some hate dairy, some hate seafood. Some people have food allergies, intolerances or sensitivities. Some people lack the enzymes to break down various kinds of foods, or have reactions to foods in the nightshade or brassica families. Some people have phobias or aversions to particular scents, colors, shapes or textures. So there's no one diet that works for every single person. I eat 80% Primal and the rest is gluten-free but doesn't strictly follow Primal for various reasons. When people ask me, I say I'm on the 'Food I can afford and am not allergic to that is within a reasonable distance from my house and is as healthy as possible' diet, because if you say you're doing Atkins/Keto/Paleo/Primal/Vegan etc someone will invariably tell you that you're doing it wrong or will pick your diet apart.
If you're looking for a healthy diet, I'd say give Paleo or Primal (or even Keto) a chance. You may read up on them and see that you can't have X because X has something in it that makes people sick and you'll say to yourself, "I eat X all the time and I feel fine!" But the thing is, you often don't know you feel bad until you feel good. For instance, I love sweet potatoes and had no idea they were causing me problems until I tried an exclusion diet. When I added them back in my guts got angry and then I realized that the intermittent gastrointestinal issues I was having were (in part) because of the sweet potatoes. Meanwhile, my husband and I had originally started a Paleo diet which meant no dairy. After being on it for a couple months we decided to incorporate dairy again to see how it would affect us because we suspected dairy wasn't an issue. I had no problems but suddenly my husband was having GI issues. So he limits his dairy and takes a supplement when he does have dairy but I can eat it with no problem. We also tried a Keto diet which was amazing in terms of weight-loss, but I developed a number of problems including acid reflux, nausea, constipation and finally kidney stones. A diet heavy in things like broccoli and spinach can lead to kidney stones in those predisposed to them and since meat, dairy and fat are harder for your body to digest than carbs like fruit and grains, my guts were very unhappy. So while I would have loved to stay on a Paleo-Keto hybrid to continue losing weight at that pace, it just wasn't the best diet for ME.
So, try an exclusion diet. Slowly add foods back in to see what affects your positively and negatively. If a Paleo, Primal or Keto diet work for then stick with it. But if they leave you feeling miserably deprived then switch over to a more inclusive diet and count calories instead. Do what works for you!