For me, the most effective are Sparkplugs; foam ear plugs which have a rating of 33NRR (higher than they used to be). They block out almost all (and in some cases all the harmful noise) from the loudest machine in my shop; the planer. You'd have to search online to find the best per pair price, but they are widely available. I'm told, though, that some people can't wear foam plugs because they are uncomfortable. Also, some woodworkers feel that they need music or some other entertainment while working. I have always felt that nothing should take my attention away from woodworking with machines, so I don't care about listening to music, etc. while in the shop. Too many things can happen when you are using saws, planer, jointers, sanders, routers, etc.
In my experience, Bose headphones are the best at noise cancelling. Over ear Bose headphones block out nearly 100% of the noise. However, over ear headphones aren't always desirable in shops because they can interfere with dust collection masks. At this point, Bose also has in-ear buds which are also very effective. None of Bose's noise cancelling ear buds or over ears are cheap; all very expensive. However, their performance is the best when it comes to noise cancelling.
Beyond the above, you'd have to try out various brands of headphones/in-ear buds and decide which is most effective. I doubt, though, you'd find anything more effective at sound suppression than the Sparkplugs. Even though these are disposable they are not expensive in comparison to a set of Bose headphones.
