Rivendell.
there is a thread on tactics here:
kb.php?a=215The principals are the same, but that was written before the warband rules were introduced
Rivendell have most of the best heroes middle earth has to offer, though they do come at a price. The same can be said about the infantry, undoubtedly the best all round in the game, but they're expensive, so you'll always be outnumbered (unless in an unusual situation, such as a 400pts match where your opponent fields a balrog).
I've never lost with them, as they have the best all round archery in the game and a line of elves backed up with spears will be enough to kill a troll (if a troll can get that far and dodge all of the arrows you fire at him)
However, at the moment, Rivendell are best allied with the wood elves, as I find the galadhrim knights and wood elf sentinels very useful
Hope this helps,
LordElrond