は別として・はともかく: the difference
は別としてN2
Meaning
Apart from,
Past papers
Tested once in past papers
Example
手伝うべきかどうかは別としてそもそも現場にはいなかった。
Leaving aside whether I should help or not, I wasn't at the scene in the first place.
はともかくN2
Meaning
Setting aside, Apart from
Past papers
Tested once in past papers
Example
冗談はともかく、そろそろビジネスの話をしよう。
All jokes aside, let's get down to business.
How to tell them apart
「は別として」: takes the first thing out as a separate matter; often with 「かどうか」.
「はともかく」: leave the minor thing and deal with the more important one; the second part is what matters.
「はさておき」: changes the subject; leave the small talk and get to the point.