Plastic Excluders: Good for saving money, otherwise they suck.  Flimsy,
cheap, you get what you pay for.
 
Wood Bound Excluders: Sturdy.  The spacing of the wood encourages excess
burr comb which can be a clean up headache.  However, the wood can be
notched with a router to provide ingress/egress for two queen management.
I keep a few around for this purpose.
 
Wire Bound: unless the notched entrance is desired, these are my
preference.  Bee space is correct, they're sturdy and long lasting.
 
Aaron Morris - I think, therefore I bee!