I asked this in the official RuneQuest Core rules question thread, but Jason hasn't answered yet...
The Q&A pages don't really answer this definitively, but on pg 144 under Opposed Rolls, a tie means that the situation is unresolved. It does say whomever go the better result wins, which looks like a special success > normal success, crit. success > special or normal.
On pg 230, under Conflicting Rune, in the example in the right column, Vasana ties her Harmony and Air rune rolls, yet the Air rune is the winner. Opposed Rolls says she tied, but this rule seems to say the high roll wins, as in Pendragon.
So which is it? Are Conflicting Runes a special case? Or is it the difference between her rolls that determines the "better" success. Her Air rune is 90%, and she rolled 74% for that, a 16% difference, and her Harmony rune is 50%, which she rolled a 41%, a 9% difference. Both rolls were successful, but she "beat" her Air rune by a larger margin that she "beat" her Harmony rune. Is that the deciding factor as well?