depends on how much money and space youve got 100 ltr 14cfm is ample for running most air tools twin cylinder pump up faster ,and fit into the corner of garage.air chisels and D A sanders need alot of air, for diy occasional use, if you are going to to use it a lot ,150ltr static belt drive single are designed to last 12 cfm or above .get a machine mart catalogue you can compare the different specs be wary of second hand usually sold when coming to the end of life. you dont need a huge amount of air for spraying 40-50 lbs you can get low pressure spray guns run at 20 -25lbs