Pure energy is the name of the tank...
You can get it in either c02 or compressed air.
I have a AGD tank and like it,some like the air america,dynaflow,crossfire,nitro duck,angel air, theres quite a few its mostly your preference and what your willing to spend.
c02 is good for low end markers like tippys,spyders etc but if youve invested in a marker over say 600 dollars it is wise to get compressed air as it allows a more efficient shot without the spike like in c02 where your marker becomes a HOT GUN.
There are other reasons too but its too long to list all of em.