All of them.

Some are better than others, but even the best are only enhanced by reading other works on the subject.

David Irving. His agenda is well known, he styles himself as an amateur historian who knows the archives better than the professionals. The net result is his books appear to be solid scholarship, but his pro-German/Hitler bias is apparent.

In Islamic Studies that would be Bernard Lewis. Also for the love of god please don't take Tom Holland's book on Islam at face value.

Can I go ahead and use this thread to ask if The Mad Catastrophe by Geoffrey Wawro is a reliable book? It seems to have a major anti-Hapsburg bias.