I would advise on all but non-skippable instream ads.
Their viewer drop-off rate is on average not worth their minimal CPM boost.
To clarify, I meant standard-view instream ads, which are up to 30 seconds in lenght and cannot be skipped.Really?. As a viewer, I find the 15 sec non skippable ads the least annoying, and as a publisher, my earnings have increased after enabling them.