I met someone for lunch last week, and the topic of diet came up. I'm a big fan of paleo, and this is an email I wrote to him explaining why I prefer paleo over other diets:
Our knowledge and understanding of nutrition and how our bodies process food is rudimentary at best. With enough digging, you'll find a lot of "facts" are based off a single, often questionable, study that was done in the 60s or 70s.
...combine that with the fact that there is new research coming out every year that refutes research that came out a few years ago...
...combine that with the fact that the food lobby is surprisingly powerful (see: inclusion of wheat and sugar on the Food Pyramid, and even with the 2005 overhaul of the Food Pyramid, grains is still ~25%.)...
...combine that with genetic differences in how people process food (for example, due to natural selection people of Asian descent are able to get far more nutrients out of rice than Caucasians. If you had the same diet as the person next to you, but could get more nutrients out of it, you'd end up stronger and healthier. Multiply that over 4000 or 5000 years of eating rice as a staple...)
What all that boils down to is that it's impossible to say X diet or Y style of eating is the best.
What I personally like about paleo is that it's actually NOT trying to use science to argue it's the best. The argument is that "we DON'T know the optimal way to eat, but we're pretty sure a return to the sorts of foods our species has been eating for millions of years - unprocessed meats, vegetables, some fruits, nuts and seeds - is at least safe."
I don't worry about portions or ratios or counting carbs or measuring grams. I control the types of foods I eat, and then listen to my body about what I need more or less of.
It may not be optimal, but no one ever got fat from eating too much broccoli. :)