Few choices have more significant impact on the Mass Effect series than the decision on Virmire in Mass Effect 1. Players are forced to choose between saving Ashley Williams or Kaidan Alenko - a decision that influences events in ME2 as well as ME3. The crewmate who is left behind on Virmire will not be present in later games in the trilogy, so players should carefully consider the benefits and drawbacks of either decision before picking their survivor.
The Mass Effect series features a unique balance of story and combat, combining narrative RPG choices with action-oriented gameplay. Mass Effect 2 and 3 in particular focus heavily on combat compared to Mass Effect 1, so it's a factor that players need to take into account when faced with the question of who to sacrifice on Virmire. Although Ashley and Kaidan are not crewmates in the second game, they can fight alongside Shepard for a large portion of ME3, and selecting the character whose class most benefits Shepard can help players out in the long run.
While the overall story of the Mass Effect trilogy plays out similarly regardless of who survives Virmire - the survivor can become a Spectre in ME3, and they both serve the same role on essential missions such as the Citadel coup - the personal character development of each crewmate is vastly different. Kaidan and Ashley are both romance options in Mass Effect 3 (Ashley for a male Shepard, Kaidan for male or female Shepards) and grow to have unique friendships with both Shepard and the rest of the Normandy crew.
The Benefits Of Kaidan Versus Ashley In Mass Effect
Ashley starts off the series as someone inexperienced in regards to working alongside aliens. Given her family history involving the First Contact War, she distrusts and doesn't understand many of the species working as part of Shepard's crew. She doesn't hate them, she explains, she just doesn't trust them over humans. By Mass Effect 3, however, Ashley grows to form deep and trusting bonds with the aliens aboard the Normandy, especially those who were present in Mass Effect 1 such as Garrus and Tali. In combat, she represents the Soldier class and can bring some heavy firepower to a fight. Players who focus more on tech and biotic abilities may find it helpful to have someone capable of hanging back and providing damage from afar. A male Shepard who romanced Ashley in Mass Effect 1 can carry the relationship over into ME3, as well.
Kaidan is a supporting fighter in contrast to Ashley. He combines biotic and tech abilities and functions similarly to the Sentinel class. In Mass Effect 3, he's arguably one of the stronger crewmates to bring into a fight - particularly if players are focusing more on gunfire than complementary abilities. If Shepard is a Soldier, they can get good use out of Kaidan's wide range of skills. He also receives some story development between ME1 and ME3 - while in Mass Effect 1, Kaidan can only be romanced by a female Shepard, he opens up as a romance candidate for male Shepard by the end of the trilogy.
While both Kaidan and Ashley serve similar functions in the grand scheme of things, the unique dialogue, story and combat content provided by either crewmate varies drastically depending on who survives Virmire. Players should consider these various factors when making this crucial Mass Effect decision.