You need to look at every type of application. Trying to do a full front vector print on a black shirt for 48 shirts with a
dtg printer is not the most profitable way. I have a section in the
dtg 101 Guide I released that talks about this concept. You might want to skim through it even though I made it for people looking to buy a
dtg printer. Here is the link -
www.multirip.com/dtg101.pdf.
In some cases, you might want to use a plastisol transfer or just contract it out to a screen printer. If you are trying to print a photo to a polyester shirt, then you probably will want to go with a dye sub transfer. 50/50 shirts might work best with an inkjet transfer for short runs. It just really depends on what type of graphic you are working with (vector vs. raster vs. photo), the type of shirt printing to, the color of the shirt, the quantities desired and how much time you have to fulfill the order.
Hope this helps.
Mark