4 troop types: Mounted, Ground, Ranged, Siege. Basic roles: Mounted=PvE monster hunting + PvP vs Ground (highest attack/speed); Ground=PvP vs Ranged + resource gathering (2nd highest Load, high Defense/HP); Ranged=PvP vs Mounted (best Range, weak Speed/Defense/HP); Siege=PvP vs Ranged + resource gathering (highest Load, longest range, weakest Attack/Defense/HP). Rock-paper-scissors at equal tier/buff: Mounted beats Ground, Ground beats Ranged, Ranged beats Mounted; Siege beats Ranged but loses to Mounted/Ground, and is 'extremely' strong (kill rates 10-23x) vs any lower-tier troops. Close-combat types (Mounted, Ground) beat long-range types (Ranged, Siege) if they can close the distance. Siege range increased in a 2020 update by tier: T1-4=1,400, T5-8=1,556, T9-10=1,711, T11-12=1,867, T13-14=2,178 (ranged troop range is 500). Combat formula (per site admin comment): Number Defeated = Attack x Number of Troops x Troop Compatibility Coefficient x (Attack/(Attack+Enemy Defense)) / Enemy HP. Troop compatibility coefficients (attacker:defender): Ground vs Ground/Ranged/Mounted/Siege = 1/1.2/0.7/1.1; Ranged vs same = 0.8/1/1.2/1.1; Mounted vs same = 1.2/0.8/1/0.9; Siege vs same = 0.35/0.4/0.3/0.5. Power (a rough strength estimate) is identical across all 4 troop types at the same tier despite differing Attack/Defense/HP splits. T12 troops are widely believed unusually strong because the game's starting 'City of Throne' troops were coded as T12.
Original research source: Evony Guide Wiki