Board Thread:General Discussion/@comment-31176316-20170208054606/@comment-31481772-20170526120045

In that case, I feel that Apollo is the strongest. (Sorry this is copy-pasted from an answer I wrote in the discussions.)

Apollo has a wide range of powers. He also has qualities that are effective in combat, such as archery skills, great reflexes and speed. Apollo is also a decent swordfighter and hand-to-hand combatant.

I think Riordan himself says the following things: 1) Apollo beat Ares in a boxing match.  2) Apollo beat the super-fast Hermes in a foot race. 3) Apollo nearly defeated Hercules in a fierce fight at Delphi.

The other Elder Olympians - Hera, Hestia, Demeter and Aphrodite - are relatively peace-loving and non-aggressive. Apollo would obey them out of respect, at most, not out of fear of their strength.

Apollo's biggest competition would come from Artemis and Athena. Either of them could probably beat Apollo in a fight - using skills and trickery. But I think Apollo is stronger than either of them.