I always recommend customers go with what they know. Since you have people that can maintain and optimize both platforms, my inclination is for Solaris. Troubleshooting problems on Solaris tends to be easier since Solaris comes with many useful tools (e.g. ldd, truss, adb, snoop, pfiles, etc.) by default. Additionally, since Solaris does not require anti-virus software, there are always a few more resources made available to LMS on that platform.
