IK Obi
Haven't tried the CA-2A, I'd love to hear a shootout with someone who owns both...
I have not bought the IK white plugin but I have check out the demo and compaired both of them and other LA plugins.
IK white is also one of the best LA emulations out there. Same class as UAD, WAVES & NI Softtube. But I feel the CA-2A is one lever above both WAVES, UAD, IK and Softubes. And when it comes to functionallity, sidechain, fully modeled "R37" HF Pre-emphasis control, dual photocell reset modes (Classic & Fast Reset) no one beats it. Its the best sounding and versatil LA out there on the market right now. Sidechain I love it!
Best Regards
Freddie
http://www.cakewalk.com/products/CA-2A/