Why Other Shells Didn’t Click

When I first started playing Marathon I decided to use the Destroyer as my main Shell. I really like the idea of the Destroyer's movement capabilities as well as the Search and Destroy ultimate that just seemed so damn fun to use (I mean who doesn’t like obliterating things with rockets?). And so for the first few months I only played Destroyer.
As time went on I did get better at the Shell, but it became apparent that I may not have the technical capabilities to maximize the Shell to its fullest potential. The Destroyer has a very high skill cap, similar to Vandal, and while it was fun to play, my PvP success rate and extraction rate was not very good and my Vault was looking pretty bare.
At this point I actually tried Triage, and while it was fun keeping my teammates alive, especially when playing with in real life friends, I would still struggle in firefights and more or less feel useless in PvP - especially when things got to be close quarters where Triage really struggled.
I would constantly get caught in poor positions just because, honestly, I'm not that good at the game, and as the skill level of Marathon in general increased I struggled to keep up.
So I started to play around with every shell to see if one clicked with how I like to play, and it didn't take long to discover that Thief is actually the Shell for me and is also a Shell that I would suggest to anybody that is struggling with PVP in Marathon.
Why Play Thief?
The reason Thief changed everything for me is pretty simple: the Grapple Device.

This ability has saved me so many times it's actually unbelievable, and it also has allowed me to completely flip a firefight nearly every Run. Out of all the movement abilities in the game, the Grapple Device moves you by far the most distance. Not only that but it gives you insane verticality that no other Shell in the game can match.
My main uses of the Grapple Device are to gain the high ground during a firefight where I'm on the same level as my enemies, use it to flank enemies quickly and efficiently (especially with the swing mechanic you can really make a 180° circle around your enemy and end up behind them), and also use it to just simply disengage when I'm caught off guard by a team that might have a long sight line on me.

Not only is this a great ability during firefights but it's also a great ability to just navigate the map allowing you to always keep The high ground when entering points of interest.
When you combine this with the Recharge Track in The Cradle you can use the Grapple Device ability extremely frequently making it truly one of the best abilities in the game.
Thief Shifts Your Mindset
But Thief taught me something else about playing Marathon, and that is to take things more slowly.
When playing Destroyer or Vandal, generally I would rush around the map using the movement abilities to get from point A to point B quickly. But that would result in me getting caught in no man’s land by other teams. Thief has taught me to play slower.

You have a recon drone that literally forces you to stand in place, slowing down a Run, but it allows you to scout the map ahead of you to make sure that you have all the information you need about a POI that you're approaching. This play style - while not as exciting - has resulted in substantially better results as far as extracting and gaining loot.
Thief Gets The Best Loot
Speaking of loot, Thief has one of the simplest passives in the game that's also extremely powerful. The Finer Things, Thief’s passive, boosts your weapon handling and Grapple Device recharge rate you fill up your backpack. On top of that the X-Ray Visor allows you to quickly pinpoint where the most important loot is so you're not wasting time in a POI, and instead are looting wuickly and continuing around the map.
This has been super useful with my squad as many times we would get to a POI and spend too long looting, allowing another team to creep up on us while we loot. When I play Thief with the squad, we get into a POI, we loot quickly and we get out before another team can catch us off guard.

X-Ray Visor also makes Strongbox/Armory Keys a lot more useful as you can always see where the best loot is in the room. In general my loot quality when playing Thief is so much higher than when playing any other class in the game and I owe all of that to the X-Ray Visor.
X-ray Visor is also very nice against USEC enemies, and while it's not as good as something like the Destroyer’s Search and Destroy, it is very nice to have something to help you deal with Wardens, Commanders, or other difficult robots.
Most Important Thief Tip
And one final thing… you can LITERALLY PUT A CLAYMORE MIN ON THE THIEF DRONE, fly it into another squad and do massive damage with them which might be the single most fun thing to do in the entire game!
If you're struggling with Marathon, if you're having a hard time leaving a map with solid loot, I would highly suggest checking out Thief, running some free loadouts on her, and getting familiar with her play style.
She's more than just a solo option - she's amazing in a team setting - and I've been the reason my squad completely flips fights, as well as getting my team all the juiciest loot in the game. I don't think there's any going back to any other Shells for me.
I'll see y'all on Tau Ceti!