Well I used to main metaknight and theres really not much you can do as a CP for him. there probably aren't any pickable stages where Shiek gets an advantage to metaknight, but there are stages that make the match less one sides to metaknight.
Im not sure if what im going to write about stages to pick is really towards helping out sheik, but they i know it'll help a bit cause i've experianced these things
we all know MK is light, so picking stages where there are small boundries (low ceiling especially) make the match much easier on your side, cause then he dies easier.
FD is a bad place to take metaknight, the stage is big so you can needle his *** a lot, but in the end its not going to help much. MK gets a lot of chances to shuttle loop you becuase of the free space.
battlefield is probably a better stage to pick against metaknight. shiek naturally does good there, but so does metaknight, but it gets rid of the chance to constantly shuttle loop, also shieks air attacks come out fast, so it isnt hard to use the platforms to your advantage to beat on metaknight, only problem is that we all know metaknights air game is just to good.
to be honest, I find yoshis island and smashville good places to fight mk on. I remember hating those two stages when i was playing as metaknight, its something about them that gets him killed fast.
yoshis island is a small stage, so you wont be able to hide from metaknight or anything, but the lack of a good platform (yeah. i dont think that big platform in the middle of thestage is very good at all) keeps MK from abusing platforms to combo you and such. plus you can wall cling on yoshis island, it probably wont help you, but hey wall clinging is cool
smashville im not sure why. i just hate that stage as metaknight. I think the reason he gets beaten a bit harder on those two stages is the fact that they are small, metaknight is always going to have someone on his *** that way.
you might have noticed i only listed neutral stages for the most part (i cant remmeber if i mentioned lylat, and im to lazy to check) thats mostly because almost all the CPs we have gives metaknight some kind of advantage, so i looked things over on my game and tested mk a bit and it seemed like all the neutral stages bring MK down just a bit, if anything.
This probably didnt help much, but it might open more discussion that could help us figure this one out.