Screen printing has been around for quite some time and even though new techniques are constantly getting developed, there are two main methods still in use. Water-Based Ink and Plastisol.
Water-based Ink has little to no effect on the feeling of the garment. It blends in with the fabric almost perfectly and is highly durable against time. As the ink is water-based it's less suitable for darker shades of textile as it's having difficulties being visual. So, if that's what you're looking to do then Plastisol it is -->
Plastisol is, instead of water, based on plastic. That gives it a brighter look and the ability to be used for more exact shades of color. Unlike the water-based ink, Plastisol is printed on top of the fabric instead of blending into it. This of course gives it a bit more rough texture and less protection against wear and tear. As an example, water-based ink will make it through years and years of washes and might only lose some spark, whilst Plastisol will start to crack and sometimes even fall off.
Both methods have their charm but I prefer Plastisol. Which one is your favorite?