You'll see a lot of debate on here, but nobody can truly tell Ya what's best because it all depends on your play style. Suros is a great AR as it has a very low learning curve. Great in all situations and can handle large groups. Thorn is a very high damage hand cannon that can shoot at pretty far ranges. Great in mid/long rang combat. Not too great firing from the hip and can't handle large groups. Red Death (I don't own this one but from everything I've seen and read on) is great for Ned/long range and can handle small groups with its health regen. The Last Word is fast and can handle small groups in tight spaces. Terrible for long range combat. MIDA is amazing for mid/long range but can be difficult when running and gunning. Hard pressed up close. These are just the relevant primary exotics (as that's what I tend to mostly use in pvp).