dunno about the torrent... but i took that pool to.
my first power was PG, and it a good power to hold lts and minions.
after that i took dark blast, it does moderate damage and debuffs mobs accuracy[i slotted it 3xdam 1xacc 1xdebuf]
after that i took the TT that holds more mobs at the same time and debuffs there hitpoints.
i like this set verry much with my scrappy...
and for me its verry usefull.
Body Mastery for me, tried the other two but never really like them. I have a sort of hold in ToF (DM/Regen) so I never really needed that. I quite like the weapons mastery due to caltrops, very nice to auto slow AVs.
Body mastery is good though because you get the extra accuracy of Focused Accuracy, which unless you are an MA/* is always going to be useful. The end recovery power is supposed to be quite good but as a regen I've never bothered. Laser Beam eyes is not bad and gives an interesting pull and it looks cool. Never got the last one or even really looked at it but its another torrent, with IIRC a good chance to knockdown.
Torrent from dark:
very big knockback and seems to have a wide cone, doesnt do much damage though, has a long range.
useful for scattering the mobs and giving you a bit of breathing space, good for protecting anyone thats in trouble throw torrent at them and the mobs literally go flying. however not really a good opener due to the mag of the knockback (although, its very good at sweeping away the minions so that you can take down the one boss who resists the knockback).
Torrent from Energy:
High chance of knockdown, knocks back on weaker foes, has higher damage than Dark Torrent but a shorter and more narrow cone.
very useful as an opening move to deck all the group in place so you cna get in the thick of it for your pbaoe attacks, you can normally get that attack done while the mobs are getting up, so its like a couple of freeby hits.
Wepaonon mastery, i've never used as i heard it was too pants.
Dark Mastery i found myself slipping more into control and suppression rather than out and out killing, plus all the extra toys just confused me 
(although it was good fun)
Body mastery this is what i stuck with because of energy torrent and focused accuracy, with FA 3 slotted for tohits you dont need accuracy in your attacks, allowing you to slot for recharge or secondaries.
@ExtraGonk
I orginally took dark mastery leaving out torrent and taking the other 3.
Loved pet gaze and TT, was so so about dark blast.
I respecced into weapons because i hated being slowed by caltrops, but havent played it much. Not sure i like tho.
Still hve 2 respecs to use and i am tempted to respec back into dark for the holds.
Got to 41 the other day with my lil' ol' scrapper and got the option to choose epic power pool, not really sure what to pick I looked them through and decided to get the darkness mastery for the acc debuffs and immobilize. Chose "Torrent" as my first epic.
Any tip on how to use it wisely? Did I make the wrong decision?
Or, does anyone know of a guide to epic power pools for scrappers? Tried to find one but without luck..