Do I choose CO2 (Carbon Dioxide) or compressed air?
Paintball has a history of utilizing CO2 as a power source, this is less so today. CO2 is cheaper and lighter than compressed air but allows for less shots per tank and lesser shot accuracy in cold weather. Compressed air tank allows continuous consistent shooting and is not weather dependent. Note that some paintball markers (guns) can only operate using CO2.
Do I choose aluminium or composite tank?
Aluminium tanks are smaller and cost less but tend to weigh more than a composite tank. Composite tanks can hold more pressure, hence allow more shots per tank in comparison to aluminium.
Do I choose a 3000psi or 4500psi tank?
Tanks are pressurized up to the specified working pressure of the tank, typically for compressed air applications in paintballing the options are 3,000psi or 4,500psi. The aluminium tanks are rated up to 3000psi maximum. Composite tanks are rated up to 4500psi; handling more pressure therefore yield more shots per tank. Shot counts vary between markers (guns) but most markers get about 10 shots per cubic inch at 3000psi and 15 shots per ci at 4500psi.