Irish: Expressing "the best known X".
I am trying to figure out the sentence pattern for the sentence, "White Oak is the best known oak of all." I found the following example sentence on focloir.ie.

This is the earliest known example of poetry.
= Seo an sampla is luaithe den fhilíocht a bhfuil eolas air.

The book "Teach Yourself Irish Grammar" also has the pattern:

Mairéad is the secretary.
= Is í Mairéad an rúnaí.

Using both of these as guides, can I express my sentence as this?

Is í White Oak an dair is fearr de na daracha a bhfuil eolas acu.

Question

Irish: Expressing "the best known X".
I am trying to figure out the sentence pattern for the sentence, "White Oak is the best known oak of all." I found the following example sentence on focloir.ie.

This is the earliest known example of poetry.
= Seo an sampla is luaithe den fhilíocht a bhfuil eolas air.

The book "Teach Yourself Irish Grammar" also has the pattern:

Mairéad is the secretary.
= Is í Mairéad an rúnaí.

Using both of these as guides, can I express my sentence as this?

Is í White Oak an dair is fearr de na daracha a bhfuil eolas acu.

Answer

Good attempt, but you need the preposition "ar" rather than "ag" (otherwise it seems like the white oak is the most knowledgeable oak).
I would say:
Is í an dair bhán an dair is mó a bhfuil eolas uirthi.
Tá an dair bhán ar an dair is mó a bhfuil eolas uirthi.
or perhaps:
Tá an dair bhán ar an dair is mó cáil. (this could also imply that this species is highly renowned)