The Pistol is the first weapon in the game that comes with infinite ammo. There are 2 upgrades that come with it. Upgrade 1 is Damage Increase and Upgrade 2 is Speed Increase.
The Pistol delivers low damage, has a medium firing rate, and infinite ammo. There is an upgradeable version called the Dual Pistols which does medium damage, high firing rate, and also comes with infinite ammo.
It is recommended to buy Upgrade 2 right off the bat so you can have an advanage over the other players. Dual pistols are also recommended because it makes it quicker to kill others and is free to get when you enter the lobby aside from the fact that the upgrade requires XCash.