Location: A realm outside of existencePrep-Time: none
Both at full power
Solaris one-shots. It eats dimensions in mere seconds, and it can only be destroyed by attacking it's consciousness across time. Not to mention being fully omnicronological, omnidimensional, and omnipresent, he's pretty much beyond Tabuu's reach.
Sonic in base form was able to damage Tabuu, but he had to go Super in order to fight Solaris in the present. Tabuu gets God-Stomped.