There are so many many diets out there, and arguably the DASH diet is one of the elder statesmen of the diet world. It was extensively studied in 1997 at Harvard University, and spawned several other good studies (OmniCarb, OmniHeart, DASH-Sodium, etc.).
I find DASH fairly straightforward: it is Mediterranean-like, reasonable, intuitive, and it comforts me to know that there is very good evidence that it reduces the risk of strokes, kidney disease, dementia, and heart attacks. It is effective: It can lower the blood pressure as well as medications in four weeks.
If you are trying to avoid metabolic syndrome (high blood pressure, high lipids, large waist line, high BMI, high blood glucose, high insulin), then this is the diet for you.
If you are on a psychiatric medication, then this is the diet for you. Most of the psychotropics put you are risk for the metabolic syndrome because weight gain is often the side effect.
It will take more than DASH to stay healthy (i.e. exercise), but its a great place to start!
Note: The last article below is an informative, 2014 interview with DASH’s original researcher, Frank M. Sacks, MD.