My opinion parts from the lower to middle tiers of the troop tree for two main reasons. First, because High tier is very hard to achieve and not really representative of the faction judging from the player's (me

) point of view. And second because lower to middle class troops are the backbone of your army.
Other than independent troops you can rescue, like Noldors and peasant/pendors, or mercenaries at taverns. I think the most balanced faction is the kingdom of Ravenstern. They have decent middle infantry and archers, their cavalry is pitiful until they reach knighthood status which is relatively easy to achieve. + their geographical situation allows them to have a whole flank covered, thus giving them a unique advantage over the rest of the factions. That and the fact that mountain bandits at the north end of their realm are great sparring troops for the starting commander and a great source of peasant troops.
Sarleons have very weak infantry until they reach the armored footman status and then they are not so great either. Their archers are fairly as skirmishers and very good as longbowmen but you have to deploy them in numbers above 15 to really make a difference. Their cav. suffers the same problem as the ravensterns and, other than their extensive use of blunt polearms, can't find a real difference between both. Their position is too extended and vulnerable on all sides. I don't like this faction and the only troops I rescue are the longbowmen and the ocassional halberdier. Sarleon halberdiers are the best troops of the game when you are defending a castle imo.
Fierdvains have very good middle infantry and their archers are good melee troops too due to their massive use of axes, but they all easily fall prey to condentrated bow/xbow fire and to middle to heavy cavalry. Their cavalry is quite funny cause they have to change gender in order to become so

, good fast, light cavalry for harrasing loose formations and stragglers but can't stand a chance angainst the Rav and Sarleon heavies or the D'shar mounted archers. Their position on the map is not as bad as the sarleon's but not very enviable either sice they are flanked on three sides and the northern raider armies prey on their caravans constantly.
D'shars were my first choice when I started the mod for my chatracter is a mounted archer but they have very weak infantry due to their lack of shield to protect them against misiles, and while they have pretty good archers, which can reach their veteran status very fast, I have to agree with a previous poster that they have light armor too and have a high rate of casualties in battle. Raider and horseman levels are very good light to medium mounted archers with decent melee capability against less than heavy cav. but their cav. tree simply lacks the heavy tier to support them and they are toast if caught by middle to heavy infantry or too many spears and misiles. Their position in the map is protected by sea and mountains on its north and east flanks + the other two flank have passages which can delay an invading army. Not a bad defensive position but nothing expectacular either.
At last the Empire has the best anti cav. light infantry and the best melee middle infantry of the mod. Their xbowmen are good but their slow rate of fire wont help much against large numbers of bowmen and/or fast cavalry and MAs. Fairly good support xbow cavalry but again they are good as flankers only. This is an infantry heavy faction and the only one where I prefer not to upgrade beyond legionaire level. Map position is big and hard to defend wit the added threat of permanent snake cult bands, great source of income once you get a half decent party btw, and the ocassional Noldor raiding band. But plenty of bandits + red brotherhood and some heretic cult parties that can help you improve and feed up your command.
Hope this helps.
Cheers!