5. Rescue - Rescue is a favorite on defensive teams in PvP, but that speaks more to her ability to prolong a match rather than to her effectiveness. This isn't to say she ineffective. She is easily the best support hero in the game and is excellent at limiting tactical options of an opponent. She doesn't have a lot of value in PvE where she causes battles to last longer rather than end quickly, but in PvP, especially when you aren't controlling her, she is a dominant force that may occasionally cause your opponent to forfeit just to avoid a long battle.
4. Havok - When left alone to his own devices, Havok owns in PvP, but most smart players will never leave him alone. His power is countered by the fact that he is incredibly flimsy when a tactician acts before him and tacticians are very common in PvP, including his incredibly effective brother. Unlike Rescue, he makes up for this by being reasonably effective in PvE as well. One hit kills aren't quite as useful in PvE as they are in PvP, especially when that attack will make Havok lose his next turn, but he also regenerates stamina, which mean he is good in long fights.
3. Magik - Magik is by far the best Special Operations hero for PvE boss battles. She has two different powers that allow her attack incorporeal or phased opponents and one of those powers never misses. Additionally, she can strip buffs from enemies and apply up to three different ongoing damage effects at the same time. Many of the hardest bosses in the game are incredibly susceptible to her skill set. She is a modestly effective spoiler character in PvP as well, but the main reason to own her is for ease of PvE.
2. Ares - The God of War, Ares, has a single ability that makes him a valid option for almost any hero team. While he is alive, whenever any character on your team makes a single target attack or is subject to a single target attack, the other two characters have a chance of following up on that attack against the target or attacker. This usually amounts to one to three extra attacks per round, which is like having extra team members. This is especially powerful with characters that have nasty status effects on their basic attacks. Until the Combo Breaker power on Iron Fist was fixed, Ares could be found on about one of every three PvP teams.
1. Emma Frost - Emma Frost is such a good Special Operations hero that she has received multiple reductions in power and still stands out as one of the best tacticians in the game. Her impressive suite of abilities was made even better when she received an alternate uniform that randomly buffed allies and stripped negative status effects, including stun, at the start of each ally's turn. In PvE, against non-mechanical foes, she is an absolute powerhouse, using Psychic Tap to effectively one-shot most enemies. In PvP she has a high damage area attack that can be repeatedly spammed as long as the enemy doesn't include any heroes immune to psychic attacks. She is the primary reason for the popularity of Magneto and Juggernaut in PvP and even when they are present in a battle, she still has a chance to pull her weight. As a final added bonus, owning Emma Frost allows you to potentially earn an unique E-ISO for Magneto.