Bonner's a role player. he's largely inconsistent (don't count GSW series because that was a horrid matchup for him and 90% of the team) because he's a role player and those usually play well at home as opposed to away.
Manu's been inconsistent as Uwe noted, but those are two different roles. Manu's expected to be a superstar and has to take more chances/risks in his game than Bonner, who's there to do one thing and if he doesn't do it he'll be criticized heavily. Ginobili's there to take over a game (even at this stage of his career) while Bonner is there to stand around and make the 3 ball (while improving on rebounding and giving a shot or two).
both of those guys can face criticism, but it's not technically fair with what they've been given so far a bit especially when you realize both of their roles.
if you wanna talk about someone widely inconsistent, you throw in Gary Neal's name. he has more of a role than Bonner and less than Manu and he's given squat.