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Castle is good for a confident push. Double-shot, upgraded archers in the early game allow you to easily defeat neutral creatures. They are built quickly; they gain excellent speed with upgraded griffins and later, archons. Orrin and Valeska are archer companions, Turis is for melee characters. I will not consider Adel and Mullich, who are banned in tournaments.
Rampart is an excellent "defensive" castle. Strong screamers of levels 1-2 and 5-7, frankly powerful upgraded centaurs, frankly powerful upgraded elves. Mages will have a hard time if they wait for the full upgrade, because one creature has immunity 1-4, one has 40% resistance, one gives an aura of resistance, and another increases the cost of enemy spells. The downside is that the troops are not very mobile (4 stacks of 2-cell units) and there are some slow units in the troops (gnomes, dendroids). For an archer, the initial choice is Ivor, for a melee character for long battles - Thorgrim (anti-mage) or Mephala (armor master). We will not take into account Rilanda and Kirra, who are banned in tournaments.
Tower is an extremely strong castle in the hands of a skilled archer. Master gremlins provide a relatively easy start to the game and quickly defeat slow, non-shooting neutral creatures; upgraded gargoyles have good speed. Excellent magical support thanks to the library and the presence of creatures such as Archmages (-2 spell points per cast), Master Djinns (3 random positive casts on themselves). In a fully upgraded castle, there are three archers, which allows you to create an archer army, supplementing it with slow gremlins as needed, which, with the support of nagas, djinns, and gargoyles, will tear the enemy to shreds. The best choice for the start is unknown, honestly, because I am not a Tower player. As far as I know, Kira and Solmyr are banned, and Fafnir will be useful with his specialization in a long game.
Inferno is powerful in skilled hands, as they say... One archer (Magog) works very peculiarly, stunning both allies and enemies. Cerberuses and Archdevils with retaliation somewhat improve the situation; Ifrit Sultans with a fire shield also cause headaches for any opponent, however, the other hellish creatures are frankly unremarkable. The best tactic is to breed demons using the ability of upgraded pitlords. The best starting hero is Octavia (+350 gold), Kalh (many demons = better relations with neutrals) or Ignath (a large stack of imps and devils hits hard).
Necropolis is difficult at the start, but unbeatable (in skilled hands) in a long game. Attention should be paid to dread knights, upgraded liches, and vampires (their upgrade is banned in tournaments, if I remember correctly). Once a certain core force is assembled, all that remains is to run around and beat everything that moves. What doesn't move - make it move and beat it. The best starting hero is Galtran (many skeletons from the start), Isra or Vidomina (the specialization with the strengthening of Necromancy is decisive). It is also worth paying attention to Nimbus and Clavius (+350 gold) - they will be good, profitable units.
Dungeon is pure evil. Two decent archers, built quickly, and fierce upgraded harpies in the first week provide a good and quite powerful core of the army. The best starting characters can be considered Shakti (the most expensive starting army among all heroes) and Lorelei (specialist in harpies). We will not take into account Jeddite, Alamar (specialists in resurrection) and Gunnar (specialist in logistics), who are banned in tournaments.
Stronghold is a castle for a rush. With resources and the construction of a wolf den from the start, creatures can be obtained as early as the second day of the game (birds --- creatures). The city is focused on attack, so most of the units hit very hard - even though they are not expensive. Crag Hack and Gundula are our best friends in a long game, and Gretchin and Tiraqsor are for a planned rush.
Fortress is a city designed for defense in the long term, but also excellent for rushes. Wyverns can be built on the first or second day (if there are resources) - it depends on the presence of a lizard den in the city. In the second week, the surrounding hives are cleared, after which the number of wyverns grows much faster than the enemy would like. Brokhild is a specialist in them and will be useful for the final rush. A quick start can be provided by Vistan, Dragon, and Bron (the latter is apparently banned in tournaments due to access to level 4 creatures from the start).
Conflux is a fierce castle for a quick start and overwhelming development. The color of the army is upgraded fairies, which have fierce speed, flight, and retaliation. The fairy army, in skilled hands, breaks through any non-shooting neutrals that are slower than them by 2. The growth of phoenixes and firebirds also does not particularly please opponents - it is twice as high as in other cities. The best hero for the start is, of course, Grindan (+350 gold, earth magic and slowness from the start). Ciel and Luna, who are banned in tournaments, are not taken into account. It should be noted that in tournaments, Conflux is either completely banned or available without the possibility of upgrading fairies and phoenixes.