Barbirolli's Sibelius 2 with the RPO is probably more highly regarded than his version with the Hallé O. The RPO version is more extroverted -- and more well-recorded. (It was engineered by Kenneth Wilkinson and subsequently reissued on Chesky.)
FWIW, I actually prefer Barbirolli's recording with the Hallé. But any Sibelius fan needs to hear both.
Incidentally, like Larry, I'm not a fan of Herbert von Karajan's Sibelius. I don't hear anything so dire as a Nazi rally; HvK's reading is just so polished, sleek, and smooth. ... It doesn't align with my idea of Sibelius.