IMO, the best projector these days is a… flat screen TV. Projectors require dark rooms, the new TVs can be so bright that they display fine in regular light. Projectors need a clean screen (or wall) and a dark room. TV’s are their own screen.
The only value for projectors these days are larger screens (where projectors are cheaper), and situations requring an ‘acoustically transparent’ screen (where speakers must be installed behind the screen out of necessity). For a classroom, I’d suggest a bright flat screen TV.