In Bad Eggs Online, 1v1 is considered the best way to gain XP. It is even faster if you know how to win quickly. First, if the enemy is across from you, don't aim straight at the enemy unless instructed for the weapon you are using. Instead, you need to move your aim up a little. First of all, Whirligig and Mortar are best if you can hit your enemy in exactly one second. Hitting in less than one second causes these weapons to deal only 10 damage, while taking more than a second will likely result in a miss or less than desired result. I will now rank all the free weapons except for Double Trouble, which is best for a different game (1v1v1, 1v1v1v1, 2v2, or 3v3) as follows:

Weapon Rankings

Whirligig (up to 60 damage, 10 damage in less than 1 second), Required level 37
Mortar (36 damage,10 damage in less than 1 second)
Grenade Launcher in a hole that must be reached in 1 second (up to 40 damage), Required level 32
Triple X aimed at a 45 degree angle or in close range (36 damage), Required level 25
Spray 'n' Pray aimed at a 45 degree angle or in close range (32 damage), Required level 47
Gas Grenade in a hole (30 damage), Required level 4
Death from Above in a hole (avg about 30 damage), Required level 40
Shotgun in close range (28 damage if close enough)
Ion Cannon aimed straight at the enemy (25 damage), Required level 19
Machine Gun aimed straight at the enemy in close range (25 damage), Required level 8
Cannon with much lower range than usual (25 damage), Required level 30
Roman Candle (somewhere in the 20s damage)
Repeater (24 damage)
Bow (22 damage)
Dynamite in a hole with lower range than usual (22 damage), Required level 17
Air Strike in a hole (22 damage)
Vortex Equalizer (avg about 20 damage), Required level 14
Splurge Gun (20 damage)
Sniper Rifle aimed straight at the enemy (20 damage), Required level 27
Molotov ****tail (20 damage), Required level 10
Tomahawk (20 damage), Required level 22
Frying Pan next to the enemy (20 damage)
Grenade in a hole (20 damage)
Explosive Bow (18 damage), Required level 12
Bouncer (18 damage)
Throwing Knife (18 damage)
Blueberry (up to 40 damage, but usually deals 10-20 damage), Required level 35
Cluster Grenade in a hole (up to 35 damage, but usually deals 10-20 damage)
Egg Seeking Missile (15 damage)
Bazooka (15 damage)
Rifle aimed straight at the enemy (15 damage)