Berserking: 400 attack power.
400(1) = 400.
Mongoose: 120 agility, 30 haste.
120(2.8) + 30(2.2) = 402.
Yes it's 30 haste, it was stealth-nerfed sometime around 3.3.0/3.3.3 to make it less useful in WotLK (EJ has taken this into account). They have equal up-time so there's no need to weight anything further; I could have sworn I read somewhere on EJ that mongoose was potentially undervalued, but I couldn't find the post anywhere so I could be wrong.
I prefer mongoose since it helps energy regeneration as well as damage; just more utility, not a huge deal if you're laying back until 12/7. Also note that berserking can pull ahead again according to the EP values if you're crit capped, since you'd be forced to stack more hit to compensate for it, giving you an opportunity cost in lost haste/mastery:
PS: Also note that the 120 agility from mongoose ≠ 240 attack power; after counting leather specialization and assuming the presence of kings (which stack multiplicatively with one another), you get 120(1.1025) = 132.3 agility = 264.6 attack power. For the record (this is accounted for by the EP values on EJ, which also account for the crit from agility not benefiting poisons).
hows BM for EITHER MH or OH look, since most of my dps does come spell damage. i am mute specAlmost, but no cigar. 250(2.2) = 550 looks beastly, but it has significantly less up-time than berserking/mongoose, so it fell behind quickly after it was properly modeled/tested. Don't use it.