It all really depends on what type of graphic / photo / design you are printing and on to what type of fabric. Some designs are better done on different applications. Some printing techniques work better on certain fabric.
Just based on the limited information that you have shared, my gut reaction would be to consider plastisol transfers. They are ideal for short / medium runs and it gives you the ability to stock the transfers for use later on. If you screen print the designs, you are going to have to make a decision on what size, color and style of shirt immediately. Plastisol transfers are basically the same type of ink used by most screen printers (i.e. plastisol ink). It is slightly different in that it allows you to put the ink on to a special type of transfer paper that allows you cure the design to the shirt at a later time. The only thing you will need to invest in is a heat press (around $1000.00 or so). However, the number of colors in your design could make the price of a transfer be too high for what you are looking for. You are going to have to do some research on this and determine it for yourself.
Some designs just have too many colors in them. That is when inkjet/laser transfers, sublimation or direct-to-garment (
dtg) printing is the preferred method. Each of these methods have a different level of investment as well. But all the methods above require a heat press to cure the design to the shirt. That is why I suggested starting with plastisol transfers and then going from there. Hope this helps.
Mark
choosing the right print tehnique 
