IŽd say RUAG, AAS and JA are the biggest players in Germany on Citations.
I have been client at all 3... for me, AAS is the best compromise between cost and quality. Mistakes happen everywhere, and a little bit of checking by the pilot helps a lot and safes a lot of money everyhere.
I also have been client at AERODIENST EDDN (not with the CJ, with KingAirs) - which I consider to the best shop I ever was - and JA Basel (again not with the CJ).
I did ask for prices for every Inspection Document or Phase and crosscheck every bill I get. Lots of works, but worth it. (and I have received only a few invoices without mistakes at every shop)
All in all: they all cook only with water.