Texture is a very important part of creating natural looking extensions. Your best bet is to go with a texture that matches your natural texture the best. Texture can be broken down into two parts:
1) Actual wave pattern. For example, straight versus wavy.
2) Porosity. For example, silky versus coarse (also called porous).
A healthy cuticle layer will reflect light and appear more shiny. A raised or damaged cuticle layer will have a less smooth, reflective surface so will appear more dull and "textured" or coarse.
Tip: If you have damaged or porous hair, skip the silky European brands and go with hair that is more porous too. It will blend more naturally. Make sure to feel the hair between your fingers to compare to your own hair to determine if it's a good match. Don't forget that a lot of companies will coat their hair with silicone to give the illusion of silky hair. That coating will eventually wash away, leaving a less smooth product behind.
I've organized the different hair types and hair textures in a convenient chart for your reference. Refer to the chart below for help deciding where you fit and what type of hair you should buy.
European: silky to touch, smallest hair diameter/finest hair on the market, original hair color is lighter than Asian/Indian hair so blondes are less processed/damaged. Has less body than Indian hair but can sometimes have a slight body to it. Less available and most sought out so generally the most expensive option.
Asian: The largest hair diameter so great to achieve a full look. More supply so typically less expensive than Indian and European hair. Original hair color is black so light colors tend to be more processed. Generally very straight with little to no body unless permed.
Indian. The most versatile due to ranging hair textures and thickness. Can be very fine or very coarse. This hair is suitable for those who need or want body and movement. Can be frizzy and is generally body wavy to deep wavy. This hair is often permed to achieve coilier texutres like kiny curly.