Ok, here we go. The problem is that I've seen too much Sten in action and less of other guns. In addition, I only have tec9 and m4 out of these 4 guns.

Sten
Pros
+ 8 damage, 9 when upgraded
+ high clip size (32)
+ balanced rate of fire and freeze rate

Cons
- low spread (this depends on the player's combat style)
- slightly more freeze than ab8

Sten is one of the most popular spar guns to be used in Era. Sten has well balanced stats and can be easy to use. There is nothing that highly stands out with sten other than it's high clip size. The low spread can be good or bad depending on how the player uses the gun. The bullets will be more controllable but will be harder to hit bottom spar huggers. Use the sten to help close in the gap of your enemies with your low spread bullets. You shouldn't worry too much about your bullets flying into the wrong direction.

Ab8
Pros
+ 8 damage, 9 when upgraded (Needs to be confirmed)
+ very high clip size (40)
+ balanced stats (slightly less freeze than sten, needs to be confirmed though)

Cons
-Slightly less fire rate than sten
-Tight spread (once again, may depend on the player's combat style)

Ab8 is very similar to sten. The difference it has with sten though is it's slightly less freeze rate but also slightly less fire rate. Despite both have very high clip sizes, ab8 allows you to shoot more bullets than sten before reloading. Ab8 is a little less of bullet spam than sten, however you can hold your bottom spar territory for awhile if you use the gun effectively.

Note: these stats could be false as there is not enough action seen from ab8 users.

Tec9
Pros
+ Very high rate of fire
+ Quite high clip size (24)
+ Once again balanced stats, balanced freeze rate

+/- High spread (this could be a con for some players)

Cons
-7 damage, 8 when upgraded

Tec9 may be cheaper, but that is no excuse for it to be an inferior weapon. It's high rate of fire makes it a good spam gun. Along with that, it has high spread which can help you get that edge of hitting bottom spar campers. Tec9 is great at hitting bottom spar huggers, and defending your bottom spar territory. Despite being slightly weaker, Tec9 is still an excellent spar gun.

M4
Pros
+ good rate of fire
+ some spread
+ 8 damage, 9 when upgraded
+ balanced freeze rate

Cons
- 16 clip size

M4 used to be the most popular spar gun in era. It is still used today by era sparrers, the other popular spar gun being sten. M4 has one of the more high tier balanced stats. With average spread, balanced freeze rate, balanced reload, etc. Despite this, m4 lacks a high clip size for it's price. M4 takes sten and tec9 together into a balanced gun. Use the spread to your advantage but just a bit of less spread to make it slightly more controllable. M4 can adapt to many situations. M4 is your gun in terms of adaptability and balanced perfromance.

M8A1
Pros
+ considerably less freeze than the rest of the 4 guns
+ 8 damage, 9 when upgraded
+ good clip size (Someone please provide the clip size stats)

+/- Very high spread (This can be a con for some players)

Cons:
-Spread is very uncontrollable at times

An underused gun. M8a1 is a deadly spar gun with it's very high spread. Whether you're at the bottom or the top, this gun can help you hit enemies at the top or bottom. Using this gun at a ranged distance when trying to bottom hug is a bit difficult due to the uncontrollable spread. The slightly less freeze rate further adds it's potential at top spar capabilities. If you're having trouble with at the top, this gun answers your call.

Ab8 not worth but good for spar
M4 good for basing and spar
Stem most like for spar and not that good for basing
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That what I think about all 3