Field work or Solaris? If field work, urban, open or general purpose?
For Solaris or urban conflict, the Annihilator is an absolute beast. The sheer amount of firepower that thing can lay down at close to medium range is awesome, and in Solaris or an urban firefight its lack of speed and overall range don't hurt it too much because verything's already so close in anyway. In MechWarrior games it gets worse- especially in MW4: Mercs (the MekTek version at least) because you can mount two machineguns to get past the game's anti-1-hit-kill mechanism and
four Clan LBX UAC-20s for the single biggest alpha hit you will ever see a 'mech take. This thing KOs Fafnirs for
fun at close range.
For open field work, the Atlas is king. With its ECM suite and long-range capabilities, it can hurt the Annie before the Annihilator can even see it a lot of the time and its greater speed is a massive advantage here.
For general purpose field work I would also take an Atlas over an Annihilator: It's got a good punch at most range brackets to be honest, and even though it won't equal the Annihilator at close range it will be almost as effective against most enemy types while still retaining the ability to lay down some serious pain at range when the field opens up a bit. The Annihilator will often be in situations in the field where it lacks the range to just reach out and touch somebody, but the Atlas is almost never put in that position- you know when you're fighting an Atlas that however far away from you it is, you're still in danger.
Basically, the Annihilator's low speed means that even in its long-range variants it ends up being more of a specialist 'mech for defence work, while the Atlas is a much more versatile platform for general purpose combat use. For offensive work particularly, the Atlas is just plain more tactically useful.
Edited by Captain Hat, 27 January 2012 - 07:57 AM.