Henman is as consistently boring as 95% of commentators. He's not annoying though and doesn't love the sound of his own voice. Which makes him fine in my book.
I don't have a problem with any tennis commentators really (apart from Castle, who is just awful) and they are infinitely better than anyone in football by virtue of being able to construct full sentences. McEnroe being treated like a demi-god and oracle can be nauseating, especially as he speaks exclusively in Americanisms and has a few stock phrases he repeats over the Wimbledn fortnight. Never mind him also not knowing much about players outside the top ten. Of the big-name ex-players, Becker and Cash are probably the most interesting. Becker has a strange way of phrasing things at times, but it makes him and his attempts at jokes quite endearing. Sam Smith seems to be the one with the best knowledge of the game and is enthusiastic about even the less important matches. Mark Petchey is quite good too. Old timers like Barry Davies and David Mercer are always fine of course.