Part 1: The Heroes
All heroes are good (with a few exceptions) some are better than others but the reality of the matter is that each hero has it uses. When looking at a hero there are three things to look at.
1) The Stats
When you look at a hero there are three stats you see, Valor, Sprit, and Element. Each has different uses and affects different things.
Valor affects both the damage dealt and the damage taken from regular attacks. It also affects the damage on certain BM's (such as Thetis' and Richard's Armored charge attack). You will want youtanks to have high valor ratings as it will allow them to absorb more damage.
Spirit affects the damage your hero's BM does, all BM's. No BM does anything but spirit damage unless it is stated in the description. It also affect the damage you take from BM. This is useful stat not just for heroes who you want to deal high BM damage (Herc, Conan, Belle, Paris etc.) but also those support units you place in the back which can only be hit from BM attacks.
Element affects the damage you give and receive from elemental attacks. It also affects the amount healed by healers such as Asclepius. This is necessary for mages but also quite a useful stat in general as it reduces the damage you take from mages who are able to bypass such abilities such as Rally. It is also the only protection you get from elemental attacks (besides the tech) as no equipment gives element shield.
2) Troop Type
This is the most interesting part of the Hero selection process and the one that can decide whether you hire or skip over a hero. To begin with there are 5 Groups of troops. Each group has a specialization, that all troops of that type are able to do, regardless of any secondary specialization (discussed later)
Group Types - Specialty
Archers- Critical Strike These units fire from range. As such they do not take back damage when blocked by another units. They are also BM based having high damage dealing BM's (Soul Taking Arrows etc.) If you are looking for a High damage Spirit User archers are your best bet.
Infantry- Block When Infantry block they return damage equal to a regular attack of their (using their Valor and weapons not the enemies). They cannot block BM's. Infantry also have naturally high defense. They are also the only units to have abilities such as Rally. They make excellent tanks.
Calvary- Dodge While dodging does not deal any return damage. Dodging has the added bonus that you are able to dodge BM's. They have weaker than average defense but a greater attack because of it. They are the only unit to have such BM's as Armored Charge Attack.
Machines- Valor Machine specialize in Valor by which I mean they have high attack or defense. A machine with the same weapon will always deal more damage than any of the above troops (exception is the armor chariot). Most Offensive machines have a secondary specialization of Critical Strike. However they are also blocked/dodged more often than other units, and have low defense. (exception armored Chariot)
Mages- Element Mages are unique. I am clumping bugler/dancer units in here for ease. Most mage type units have high elemental damage/resistance. As such they can be devastating to the earlier troop types as they have little to no elemental resistance. However all mages have a single flaw in common, they are all weak to BM damage. Getting a good spirit shield on these guys is crucial as it will win you battles.
Now each group of troops have their own specialty as show above. This specialty is common for all troop within that group. However each single troop type has it own secondary specialty, which is some that that troop type alone can do. I have noticed that certain key word in the troop type description tend to point out secondary specialties (some just come right out and say it).
Defense - Block
Mobility - Dodge
Strike Power/Offensive - Valor Hit
Raid - Critical Strike
Defensive - Valor Shield
So to compile these together you get something like this
Bellerophron - (INF) - Block/Valor Hit
These troop specialties help as they allow you to pick what formation you will want to use to accent the troops you have. For a complete list check this out:
3) The Battle Magic
Battle Magic or BM is a major part of determining what hero to use. A Bm is used when the morale of a hero reaches 100. It increases by 1/3 each hit you deal/take. Certain troops are also able to raise morale. Battle Magics fall into 4 categories: Single-Target, Line, Area of Effect and Support
Single Target: These Bm's deal the most damage hands down. They can one-hit a target easily regardless of the spirit shield. However as the name states they hit only a single player. They are best used from the back lines where you can take the time to pick off your opponents heroes one by one.
Line: This group of BM's attack players in a line either horizontally or vertical. As far as damage goes it does about half the damage of the single target to each target but can hit up to three targets at a time.
Area of Effect: This Group attack all your opponents players on the map. It deal significant less damage than single target, about 1/4th but hits up to 5 targets at a time.
Support: My personal favorite of the group. These BM's not only deal damage but have secondary effect. Some set of the Rally condition (Rally), Some Stun (All-Around Ambush), some heal the attacking unit (Mutiny Outbreak), some restore or remove Morale (Morale Absorption/Nocturnal Blitzkreig). All do damage along the lines of the # of targets they hit however they do a little less damage than BM's that just do damage.
Well that the wrap up for the Heroes section. Hope this will help you in choosing a hero. If you would like to see where heroes are found check out these two links.
Note: Cupid and Pandora's BM are listed wrong. Cupid has Phantom attack, Single Target about 50% chance of striking twice in row. Pandora has Pandora's curse, AoE with about a 20-30% chance to stun each target.