For me, I have a few but these 2 are the ones I enjoy the most:
Gregory Fremont-Barnes: Most of his books were published by Osprey and as such are short, however they are well written and provide some good insight into the topics he writes on. His account of the Battle of the Nile in 1798 is one of the best I have read so far and his book on the Royal Navy from 1793 to 1815, covering the organisation, structure, ship types etc. of the navy in the period is both a good overview and a great reference book.
Gareth Glover: His books are nothing special and as a writer he is all over the place for me, sometimes describing the subject he writes on with good accuracy and detail in a readable manner, sometimes his writing can be confusing with errors in both fact and interpretation. However the reason why I consider him exceptional is because of his work as an editor and publisher of primary sources on the Napoleonic Wars such as diaries of soldiers, official documents etc. which provide some pretty important material on the period.
Who is your favourite historian(s)? By historian I mean someone who writes books examining history, makes documentaries or contributes to the study of history in any other way. Both dead and living historians count.