I've left out the managers that were only in the job for a short while (Joe Mercer, Peter Taylor and Howard Wilkinson)
The statistics, going on Win %, suggest that Capello is the best manager we've ever had, but Sir Alf Ramsey is the only manager that has won anything.
Glenn Hoddle, Ron Greenwood and Sven all have high win percentages too.
http://en.wikipedia.org/wiki/England_national_football_team_manager