Some of my favourites
On aircraft research I would put my money on Philip Jarrett; a real gent. He hasn't written many books, but is a tireless researcher who does the best to get complete accuracy where possible, but beware; Phil doesn't suffer fools gladly.
On the RNZAF and aircraft operated in New Zealand, no finer than the eccentric but fiercely knowledgeable David Duxbury and on RNZAF personnel, the understated and genuinely kind Errol Martyn.
The dead list: The late Ray Sturtivant, another fine chap, specialised on Royal Navy aviation. Also the late Jack Bruce, former aircraft curator at the RAF Museum (although he concentrated on WW1 stuff, he was one of the most thorough researchers.) The late Peter Grosz, again specialising on WW1, but the best on German military subjects.
Here's a few I would be wary of in terms of accuracy, although I don't want to outright rubbish their efforts since as authors they all work hard, pumping out books like there's no tomorrow: Chris Chant, David Mondey, Richard Townshend Bickers, Richard Franks - his book on 75 Squadron, "Forever Strong" is known round the traps as "Forever Wrong".
For broad histories of WW2 subjects, look no further than Max Hastings. His book "Nemesis" is one of the best about the end of the war in the Pacific, also "Armageddon" about the fall of Germany is up there too. He also penned perhaps the finest biography of RAF Bomber Command, simply called "Bomber Command".
Australian Stewart Wilson produced a great series of books on RAAF and RAN types, but at times his accuracy is questionable; he edits his own aviation magazine now.
American Barrett Tillman on US naval aviation, Tom Crouch of the National Air and Space Museum writes a mean aviation history.
Biil Gunston, Tim Laming, Alfred Price, Yefim Gordon on Russian subjects; now I'm just rattling off names on my book shelf...