Not saying I'm right, I'm quite confident I'm not seeing all the replies; but if you're implying Rapid Fire gives pets haste ("you still have stampede with haste") you're wrong. Rapid Fire only gives haste to pets' focus regen, not melee attacks - which only hero/lust gives.
Or am I misunderstanding your words?
Stupid of me to say that. Ignore that brain fart. It's Berserking(me being a troll hunter) that increases melee haste, not rapid fire.
If you get lucky with procs lining up, then maybe it's better to delay the stampede till lust. But you can't rely on that. The odds of that happening are astronomical. You're guaranteed to line ALL your agi procs in the beginning. ALL of them. We have to aim for consistency.
And like someone already said, if the fight is less than 5 mins, any raid leader with half a brain would call for a lust in the beginning since ALL other classes are in the same boat we are. Everything is off cd, and will proc in the beginning. The raid will get much more benefit from lust at the start then later. Unless there is a specific healing intensive phase later on, which shouldn't be a problem with any of the below 5 min fights I can think of atm.
So yea, fight <5mins, stampede at the start (along with hopefully lust, or even without it. Still more benefitial to use it in the beginning)
fight >5 mins, stampede at start and second during lust. And I say during because if you hit it before you're losing the benefit by that much. Since stampede has a 20 sec duration and lust has a 40 sec duration, once lust is popped, just wait till you get a few procs lined up and pew pew. That is considering the fight is 6 mins roughly or higher. If it's 5 mins 30 secs or something then pop it as SOON as it is off cd for obvious reasons. It has sadly happened to me before where I misjudged the fight length and even while maintaining a solid parse, the fight was near it's end. I held on to stampede/readiness a little too long and couldn't use them fully ( No worse feeling. Except on lei shi when I (used to) pop cd's right after the last add phase. God damn that was frustrating.