what is better to raids ( most wanted to raid) and what is better to pvp????? ( i meant with shadow priest....)

If I had to pick a comparatively geared PVE specced rogue or spriest and had neither class already I'd take the spriest - UNLESS there was a truly pressing need for interrupts (though a spriest with silence will often work well too...). 

Many BC raids are simply not melee friendly and the utility of the spriest to give mana back to the healers makes them golden.  Where they can shackle (like Kara) they are even more of a blessing to have. 

There are many fights where due to the the nature of the fight, meleers will be much much lower on the dps charts simply because they have to either chase mobs or have to run out of melee range to avoid environmental or AoE damage.  It is a sad thing.

shadow priest ofc. even if the rogue can out dps the priest, the priest can still give tons of health/mana back to the party

This doesn't even make sense, they're very different classes, even for DPS.  FOA, rogues are melee, do massive amounts of DPS, and have useful abilities like stealth, sap, kick, etc.; meanwhile, SPs are ranged, do great damage at first but scale poorly with gear (due to low damage coefficients), but have useful abilities like Vampiric Embrace, Vampiric Touch (LOVE VT), Misery, Shadow Weaving, etc.

Bottom line, for a raid, one rogue and one Shadow priest is superior to two of either, because you need to have a combination of melee and range, and the various abilities.

unless your guild (which youexpect to last a long time) is bursting full of spriests, roll a spriest.  You can always pick up a rogue off the street.

Also, if you have a LOCK in the grp, he will LOVE the spriest. The stacking shadow dmg will run his dps up a LOT.

You should have 1 of each, but if you are choosing which one for a single slot and have neither, spriest will help the healer a LOT. And if you have a LOCK, will help his dps, so go spriest.

Even though spriests may be better (judging by dps and group bonuses) u got 2 admit that rouges r the most fun 4 pvp. Just spec sub. and gank people  ;)

Even though spriests may be better (judging by dps and group bonuses) u got 2 admit that rouges r the most fun 4 pvp. Just spec sub. and gank people  ;)

.....oops.  typing this on my psp, and it sux with the internet. srry 4 double post  :(