Go for Air m8, 4500 psi or 3000 your choice, Co2 will give u problems, plus its a pain to re-fill everytime, and kills o-rings. Go for a 1.1 ltr bottle as the 1.5 are really heavy. if u are planning to play more of a front player then look at .9 or .8 bottle
Air is more reliable, and easier to fill. Especially if u intend to upgrade yr marker in the future, GO FOR AIR!!! u know it makes sence lol