Hear are my plugin options to download which format works best with Sonar X2a 32 and 64 bit
 

• AAX Win-x64
• AAX Mac
• AAX Win
• Audio Unit Mac
• DirectX Win-x64
• DirectX Win
• RTAS Mac
• RTAS Win
• VST Win-x64
• VST Mac
• VST Win

Normally Vst Win for 32 bit and Vst Win-x64 for 64 bit

VST in both cases. And of course 64-bit if you're using a 64-bit version of Windows. But you can use some 32-bit plugs via SONAR's BitBridge feature.
 
Scott

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Scott R. Garrigus - http://garrigus.com - SONAR X2 Power! - http://garrigus.com/?SonarX2Power
* Author of the Cakewalk Sonar and Sony Sound Forge Power book series: http://garrigus.com/?PowerBooks
* Author of the Cakewalk Sonar ProAudioTutor video tutorial series: http://garrigus.com/?ProAudioTutor
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AAX and RTAS are for Pro Tools, AU is Mac only, and DirectX is dead, which leaves VST as the winner. 

+ 1 on all the above.

Direct X is not totally dead and should work fine too as long as you have 32 bit in 32 bit Sonar and 64 bit in 64 bit Sonar. Bitbridge or JBridge will not work with DX. Quite a few issues you see on this forum with Cakewalk synths not loading relate to trying to use 32 bit DXi in 64 Sonar.
 
A clean install of X2 64 bit will install quite a few 64 bit DXi and DX effects. - Check your plug in manager.

Brando
Normally Vst Win for 32 bit and Vst Win-x64 for 64 bit

Thanks for the advice from everyone I went with Vst Win for both, I have both versions loaded because I was not aware of bitebridge. To my surprise I like 32bit more because now I can use my plugins from Sound Forge which I did not realize I could do because I was only loading 64bit until yesterday

Sonar supports VST, VSTi, DX and DXi. You would use the 32 or 64bit version depending on your Windows Architecture and depending on Bit-Bridge, as you can use 32bit plugins on Windows 64bit.
 
CJ