I like an older Nikon flash, the SB-800. Why? Reliability...over a decade and counting...STILL works perfectly. Has nice features, good power, perhaps a bit more powerful than $79 or $89 Yongnuo or Neewer flash units. SPEED: I like this flash mostly because it uses a fifth AA battery in a special door/compartment. Not just four AA's, but five...makes a difference in recyle speed, and life of the batteries, since the discharge is spread between five cells, not just four. Makes it easier to have the five batteries in the flash, ready to go, at a moment's notice. Excellent power management, good battery life with the five cells.
FULL, 100 percent compatability with Nikon cameras, not 90% or less. Rugged. It's been durable. I use more off-camera flash than speedlight,but I have done some 100-250-shot and even a few 300-shot on-camera fill-light sessions with this flash...it's up to the task...again...instead of needing a battery pack with 8x 1.5 AA cells or whatever, I have 5 x 1.5 AA cells...gives good recylce time AND is not burdened by the need for an ancillary battery pack.
Many people have never bought Nikon flash units. I have one from 1984...STILL works....I have another from the same era...still working..I have an SB-20 from the late 80's, still working...
I look at a high-end speedlight like the SB-800 was (the top one when new) as a long-term investment, but there's another way to look at a speedlight, as a disposable, replaceable unit. Many people are satisfied with the Yongnuo or Neewer flash units.