There are five sizes and none of them is the good one. It depends on how much you get through and how much it annoys you to change a unit in the middle of a busy night.
The 666 g charger is the little one. Good for a cafe, a bar doing a few drinks an evening, or a pastry bench working order by order on kit that fits it. It goes anywhere and a spare takes up nothing.
Two kilograms is where most places end up. A restaurant with desserts on, a cafe that stays busy, someone packing for a catering job. A few different brands come in 2 kg, so usually what settles it is the equipment you already have.
The 4.33 kg one exists because some places change a smaller charger twice in a service. If that is what keeps happening, this is the fix.
The 5 kg and 10 kg tanks are a step up. They need a regulator that fits and somewhere proper to keep them, and they only pay off if you really are getting through that much.
Whatever you go for, check it against the current manufacturer instructions for your regulator or siphon. Send us what you have and we will look before you order anything.