For me the five worst actors of mainstream English movies starts with Eddie Murphy. The mere sight of this clown, with an absolutely crude sense of humour makes me mad. Besides all his recent movies like Pluto Nash have been mega flops.
Next is the British actor Hugh Grant who like typically most (but not all) Brit actors are cold and wooden. His acting consists of moving his lips (Pierce Brosnan has come commonalities in this regard).
The next three I can think off is the girly and pampered Di Caprio, the solid peice of meat and little else Van Damme and (yes) Keanu Reeves.
Keanu Reeves and Kevin Kostner have frequently been rated as the worst actors in Hollywood. But Kostner at least acted well once (in Dance With The Wolves) thereafter it has been one dismal slide with forgetables like Waterworld, Postman, 3000 Miles to Graceland etc etc.