Basically, haste scales FET very well and mastery does nothing for it, Mastery scales everything else better than haste. If you can manipulate or know in advance the exact fight timings, there are some very specific breakpoints in which if you went all out haste, it would outdo mastery specifically on single target, but the variables and risks in doing so is never going to be worth it.
tl;dr it is technically up to preferrence post-assurance and in high end gear but mastery will almost guaranteeably be more reliable and pump more damage.