Atomic Fire: Absurdly high damage, really loud charge noise, absurdly long charge time, very little afterfire delay, moderately big hitbox size, high ammo consumption.
Pharaoh Shot: Really high damage, silent charge noise, moderately long charge time, moderately long afterfire delay, moderately big hitbox size, low ammo consumption.
Noise Crush: Really high damage, really loud charge noise, very little charge time, very little afterfire delay, big hitbox size, low ammo consumption.
Homing Sniper: Moderately high to absurdly high damage, really loud charge noise, really long charge time, 6 normal-sized homing hitboxes, high ammo consumption.
Proto Buster: Moderately high damage, moderately loud charge noise that becomes silent, very little charge time, moderately long afterfire delay, moderately big hitbox size, no ammo consumption.
Super Adaptor: Normal damage, really loud charge noise, moderately long charge time, moderately long afterfire delay, 1 normal-sized homing hitbox, no ammo consumption (cannot fire until projectile returns to player).
Laser Buster: Moderately high to absurdly high damage, really loud charge noise, moderately long charge time, moderately long afterfire delay, multiple moderate-sized ripping hitboxes, no ammo consumption.
Arrow Buster: Moderately high to absurdly high damage, really loud charge noise, moderately long charge time, moderately long afterfire delay, 1 moderately-sized hitbox that splits into 6 normal-sized hitboxes, no ammo consumption.
Duo Fist: Really high damage, really loud charge noise, moderately long charge time, moderately long afterfire delay, moderately-sized hitbox, no ammo consumption.
So my comments:
In terms of damage, Atomic Fire is in its own league. Stupid 1HKO power balanced by a stupid long charge time, and a stupid loud charge noise. The closest thing to Atomic Fire in terms of power (god tier 2HKO, potentially 1HKOs) are Homing Sniper (which is highly dependant on homing mechanics, all shots must connect to deal close to 100 damage), Arrow Buster and Laser Buster (again, all shots must connect to pretty much instakill, potentially dealing more damage than Homing Sniper meatshot). Other charge weapons are within the 2HKO range, save for Super Adaptor, which deals a pretty underwhelming amount of damage for being pretty similar to other buster upgrades in other terms.
Charge noise award goes to Pharaoh Shot: a high tier 2HKO weapon, with as much power as Noise Crush and Duo Fist, without the sound penalty, and low consumption ammo. Honestly, this weapon is essentially better than the previously mentioned weapons, and is perhaps only an alternative to Proto Buster, with its fast projectile movement and charge noise that does not loop and is also pretty discrete. The explosion on Pharaoh Shot is just extra icing.
Afterfire delay is a strange one. Nothing beats Atomic Fire in this (despite it being pretty pointless since the charge time is so long), save for Noise Crush. Afterfire delay is supposed to be a gateway that prevents reaching charge state inmediately after firing a charged shot: since Noise Crush charges to max inmediately after the player absorbs one of the small shots (which in turn makes charging this weapon a gimmicky process), this gateway is negated. Couple that with a 2HKO damage and a bigger-than-average hitbox size, and Noise Crush is pretty damn good...if it wasn't so damn noisy.
Charge time, easily Proto Buster is the fastest, if we exclude Noise Crush's inmediate but gimmicky charging method. Couple that with a fast projectile movement speed and a shield, and it's a pretty good deal. Thankfully, Proto Buster deals the 2nd least damage of all the charge weapons, only second to poor Super Adaptor. The rest have a pretty moderate charge time, although it becomes relevant to mention that weapons like Arrow Buster, Laser Buster and Homing Sniper have the same charge time as others, despite being capable of dealing a fuck ton of more damage than them; especially the MM8 buster upgrades, that consume no ammo.
In terms of hitbox sizes, none of them are way too big to always hit, or too small to barely hit at all. Special mention goes to Laser Buster: lots of ripping hitboxes, in a straight line, all of which are bigger than average.
Buster upgrades are the kings of ammo consumption. Duo Fist, and the MM8 buster upgrades are specially good with this, because of their really high to absurdly high damage output coupled with no ammo consumption and moderate afterfire delay makes them more efficient than special weapons. Of the special weapons, Pharaoh Shot and Noise Crush consume very little ammo in comparison to others.