Downgrading to 2.6.0 would not help you with any problems you are having as 2.6.1 addressed many of the issues with 2.6.0.
Most of the issues on the forum with 2.6.1 seem now to be with other extensions, plugins, and server configuration, which is always the case
k2 2.5.7 at this point seems to me to be the most stable version, but those who do not have confilcts with other extensions and plugins seem to be doing ok with 2.6.1