Anwen, Talanar... they're not that great, I prefer Gilraen, Ossir, and Ilfina. Gilraen is great at the beginning and end, Ossir is good for mid-game/end-game, and Ilfina is good for everything. And Faidaen is a special case... he's always been strong, and by the way, if you don't slack off in the campaigns and run around in various arenas and rampart towers, he ends up being the strongest hero in the game:D

Added 4 minutes later
As for the ballista of the Elves... you have to level it up! If you level it up correctly, you learn Meteor Shower or Chain Lightning, and then you use "Magic Arrow" - Delebe is useless! The ballista fires three times and after each shot, it deals magic damage! The Elves have the strongest ballista in the game, and if you add Rain of Arrows to it...

Added 1 minute later
...the enemy army receives a very powerful burst of magic. Warlocks are strong, of course, but they can't do that...)))