Best party setup in this game always consist of CC + damage + avoidance.
Thus you have either the duo haste party or the 3 mages party. Both of these are the most retarded setups and enable the player to steamroll the entire game with ease and pants on head.
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The first case: Duo Haste
This one focuses heavily on physical damage. It has just so much, but just so much DPS that it has quite some potential for burst. Requires almost no micro management, aside from, maybe, positioning rogues (can avoid this tho) and some potions at times and thats it really.
The party composition will depend on what class is your warden. But you basically need:
2 mages (Both should be blood mages and one of them shoud be a spirit healer)
2 Dual dagger wielders full dexterity (either rogue or warrior)
For mages, have them learn haste ASAP. The first power spike comes at the moment that the first haste is learned. Game is hard at start, but once you get the first haste, oh god... And when you get the second... MUAAHAUHAHAHAHAHAHAHA! Get one elemental melee weapon buff with each as well. After this, the mages should focus at learning CCs, prioritizing Blood Wound, Glyph of para, paralyze, petrify and crushing prison. Then, have them learn might + wisp for extra SP. Only then, mana clash.
For melees:
Warrior: Get str to 42 with the help of gear and, if its your warden, the fade. This way, you can use the legion of the dead armor set, the best armor for offensive warrior. Focus at full dex from here and on. You will evade lots of attacks this way. Not only this, accuracy problems due to double haste are not gonna exist. Learn DW expert, then get bravery and taunt. Prioritize finesse, then progress as you wish. get the beserker and champion specialization if the warrior is you warden. Choose one of the two if it is not the warden. Berserker is better for damage (and oh god, beserk is a heck of a buff, only bad thing is its downtime, but hey, 30secs isnt that much time anyway o_o), champion is better for more evasion, accuracy and CC. Learn up to constraint for berserker and/or full champion tree. Use whatever good DAGGERS you find on the way. If you can raise their crit chance, it is realy good since they cannot back stab. And trust me, Alistair was having major problems holding aggro from my DW rogue. Keep precise striking up at all time for better crit chance.
Rogue: Do not invest a single point into str. Gear + fade will do the job for you. If its leliana or zev, gear will raise their str up to 20, so you can wear those beast rogue armor. Have them learn coup de grace ASAP. Do not prioritize lethality as you are gonna build a full dex. get cunning to 17 (fade will boost it to 22. With gear, you can get it to 30. With device mastery, you can pick all locks in the game). Get it to 22 if your rogue is zev or Leli The valuable thing of that line is in evasion. Yes. Not because of its evasion bonus, but because of the chance to resist stun and KDs. Lost the count on the times my rogue would keep on dpsing while warrior would get interrupted for full 2-3 secs due to kd or stun. Of course you wish it did not proc when you "parry/evade" the melee attack, but this anti stun or anti KD thing is a true god send. For special. learn duelist (for dueling) and assassin (mark of death). If you have leli, have her learn assassin (dueing is more to help you through early game, as the + attack and defense is useless at endgame. But its just one point and you have no headaches due to missing. MoD only helps against bosses anyway. If you think anything here fails, get a bear from ranger and be satisfied with it o-o) Learn Finesse, Coup De Grace, DW Expert, Evasion. Rest of points go into Device and stealth tree. Try to backstab if the situation allows it to be done pratucally and with ease (CCs, positioning, etc), but if its troublesome, position one rogue at N and the other at S. If one isnt back stabing, the other is doing it. If you only have one rogue, if it is troublesome, or not needed at all, avoid backstabing for that moment.
DW rogue vs DW warrior: Rogues have beter Attack speed, utility (device mastery), and the ability to backstab (which is a critical). Warriors do beter damage ONLY WHEN the rogue is not back stabing at the cost of some attack speed due to precise striking. Two rogues and two warriors work, as well as a rogue and a warrior. Just do not expect the warrior to actually tank bosses because the one that will do it is definetely your rogue. Rogues do retarded amounts of damage when backstabing.
Your melee got grabbed? Force field! Dont wanna have trouble with rogue positioning? CC the mob. Blood wound works great for crowds. Your healer should be able to heal the damage the party takes.
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3 Mages
Warden should be a mage. Morrigan and Wynne should be in your party. The last slot can be occupied with either an archer or shale.
Have your warden learn fireball and glyh of repulsion ASAP. They help a lot at early game. Then, learn mana clash.
Mages should learn fire ball, paralysis glyph. Get up to misdirection hex as well. Have them learn blood wound ASAP. Its great for damage and cc at the same time.
Enemies should die easily with triple fireball. Bosses should be dealt with easily with hexes + para glyph + triple fireball + single target damage spells. Mana clash should OHKO magic mobs and bosses. Wisp + might is great for some extra SP.
Specializations should be blood mage (the 3) and spirit healer (warden and wynne). Warden could become AW for some extra mana regen, but SH will do it as well.
Only spell combination that is worth anything is para explosion. entropic death takes too much set up. Lots of CC capability are needed to make it work without much trouble.
Tips: Learn fire ball, repulsion glyph and mana clash early so you can rape through early game. Make the other 2 mages learn fire ball as well so you have more aoe damage + cc (Knock back and KD). you only really need one mage with repulsion and warding, but having more than one mage with these is really helpful. Once you have learned repulsion and triple fireball, and mana clash, focus at learning up to misdirection hex. Affliction + vuln hex stacking is great to make boss take lots of magic damage. Misdirection will make any meleers or archers useless against you. Might + wisp are optional, but are optimal. Mind blast is great for some close range cc and cant friendly fire. Crushing prison isnt great here. Force field is really great for the moments you definetely want a target CCed till you have dealed with the rest of other enemies. All BIG aoes sould be learned last, but beware storm centuries aoe.
For max single target DPS if ya need at dragon fights: inferno + tempest + stinging swarm + curse of mortality + death cloud + 3 times stacked blood wound + fireball spam. Of course, all of this after hex debuffing.
For archer, best one would be leliana. Have her build full cun with necessary dex for bows (34 dex) and necessary str for armor (20). Aim + dueling from duelist should be enough for attack (accuracy) in addition to items.
For shale, have her learn stone aura and stand there while the mage party blows up the monsters (this is the reason why i think archer is just better. Extra damage + no need to stand still. Although shale would sure, be better for boss fights).
A tank is useless here because, if you are doing right, mobs are not getting close to your party. And if they are, glyphs. Boss? Misdirection, paralyze spam + DPS. Group of mobs? Triple blood wound + fire ball will do the job. Once you can start learning the big aoes, some rooms are basically gonna be a thing of putting a repulsion glyph at the door, casting inferno inside the room while staying out of it, move to the next one.
Full magic build for the 3 mages. Full con for shale. Full cunning for the archer.