Ok I will try to help
For silk screening it is best for long runs, they have great quality prints, but the more colors you use the more expensive it can be.
DTG is great for short runs, since you dont have screen charges, its really easy to print shorter runs of shirts. Its also great for alot of colors and high detail.
Dye Sub is great for polyester, and is the only fabric it can print on. Its also great if you plan on adding other promotional items such as mugs and things.
Heat transfers are good if you are on a budget and want to get into the business cheaply. Although if you did plastitol transfers that you order printed for you, they are better quality (as they are screen printed transfers) and allow you to apply them as you need them.
Those are the short answers of the differences
