I can only comment on BC, since i have that on my S14. Drives surprisingly well for street use, but can be adjusted from soft to hard in a few clicks. Also softer springs available if u need.
ive never tested megan.. but i reckon Megan, D2's and BC's are all much of a muchness. they all have only 'slight' Pros and cons over one - another.. i researched coilovers to death before i got decided on D2's. .. and from my research most parts on all 3 of these coilover "brands' come from the same factory / factory's... ( this is what ive read and heard so dont shoot me )
But thats not a bad thing.. as from my research ( info from heaps of international forums ) guys really rated these products comparing them to some of the really "highly" expensive brands.
So IMO go for either the brand that suits your pocket.. or the brand that suits the look of your car...