AST 3's are best they sell but AST 2's are more than good enough for clubman racing and both 1, 2's and 3's are one piece coilover iirc.
If you want anything more then your looking at proflex, ohlins, Bilstein (NOT B14's) which are all in the 2.5k upwards bracket.
Yeah I have read them. 1 or 2s better? Spring rates? Seen some using spring over shock on rear too
So defo ast