Which gives better performance: WCF RIA services or Domain Services?

I am building a new SV application which will be used from the Internet. I am expecting to

have a few users at a time, so I will need good performance.

Which is better to use:

• build from 0 WCF RIA services or
• use Domain Services?

On WC开发者_开发技巧F RIA I can set up a service behavior for ConcurrencyMode but for Domain Service I couldn't find any info about that.

Also I am a little new to this so be gentle :).