First, let's take a look at this ---> http://www.qlranks.com/ca/

And then you can start to make a list (I'm not talking about duelers or TDMers playing CA, only pure CA players)

1v1/2v2/3v3 :

#1 seriousSerbia
#2 HalItaly
#3 yrxUkraine
#4 He4rTL3sSFrance
#5 phGermany
#6 gohann_Turkey
#7 szr/f1zzdUnited Kingdom
#8 zsxUnited Kingdom
#9 cOOwPoland
#10 URAZUkraine

4v4 :

#1 phGermany
#2 v1umDenmark
#3 zsxUnited Kingdom
#4 jwzrGermany
#5 cOOwPoland
#6 visserNetherlands
#7 b0rkyPoland
#8 ormeySweden
#9 poomerSweden
#10 ouzeGermany