andromeda: resource output increase, generally useful, but since you have only one, not that much of a factor in my opinion 6/10
atalanta: travel speed increase, a gamechanger if you ask me, with this, a lighthouse, cartho and an army travel speed, your CS will go as fast as a slow transport, good luck ID'ing a CS from a fake 10/10
Chiron: can you say, hoplite nuke ready in a day? ok, ok, hoplites are not the best to turn in a nuke, but if you want to kill a lot of swordsmen, he is your man 8/10
ferkyon; 30% recruitment speed increase is pretty dang good, even better, after queing up those troops, assign him to the next town and do the same there as well, combined with pop boom and if possible a recruitment token and those troops file out of the barracks. 8/10
helen: cheaper mercenaries, really? if it would combine it with more it might mean something, but the number of mercs you can hire is small once a day, so at best you save 5k silver a day, all the while having to move her around to where the trader is. 1/10 (slightly better if you want to resummon the trader a 100 times to buy yourself a manticore nuke)
heracles: favor for winning battles with 50 BP or more, not only that, he can carry lots of loot and has good attack stats. I see potential here, but mainly if you need some favor for a certain god and you need it now. 22 favor wont cut it, but 60 at lvl 20 might mean another sea storm, or other pretty darn important spells. 7/10
leonidas; for that one city you absolutely need to keep, a turtle'ers wet dream, I am not a turtle' er and if i keep only one city I think the game is done anyway, so 6/10 from me (I know others will probably disagree, but well....)
Orpheus; a good chance for more culture, pretty nice if you ask me, more cp = more cities = more troops = more heroes to speed up those troops = win 10/10 (thou not for the first 3 cities I think).
terylea: a massive increase in silver production, nah, pretty useless in my opinion, 2/10
urephon; myth units efficiency increase, but also (slightly) lower speed than manticores and harpies, does not need a transport. make myth nukes lots more effective, can double as a leonidas in hades turtle cities and disguises said myth nukes due to speed change. 8/10
Zuretha; increases ship efficincy, your LS nukes are stronger, your bir walls are better, all in all, pretty usefull, same speed as a LS, pretty decent all around 8/10 (carthography, lighthouse will be useless here thou, zuretha is not a ship and as such will slow down those LS to normal speed)
All in all, the heroes change the whole TT to find out what is coming game and make the game more interesting in making decoys and suprise attacks.