We have a fairly wide selection of different types of cotton tzitzit garments. I didn't really realize that for some people it's too big a selection, unless we narrow things down. Yesterday we received an inquiry from someone who didn't know which type of tzitzit to buy:

I plan on placing an order today, just wanted to make sure it’s the type of tallit katan I want. I work construction and need something I can wear in all weather and while at the gym. Thanks, Nathan H.

Nathan's question is actually a bit difficult to answer, because just as different people will choose different types of clothing for those activities (construction work and gym workouts), so too different people will choose different types of tallit katan garments.

Let's start from scratch. The Torah says we must tie tzitzit strings whenever we wear a four-cornered garment. That's why we have tzitzit on the tallit ("tallit gadol") worn in synagogue during Shacharit.

The mitzvah of tzitzit is such an important mitzvah, that we are enjoined to keep the mitzvah all day, even if four-cornered garments are uncommon. So to accomplish that Jews started wearing garments like this cotton tallit katan and this wool tallit katan.

About two decades ago, undershirt tzitzit, like our Perftzit, appeared and became quite popular. They are primarily designed to be worn in place of an undershirt. Therefore, for your purposes, there's not much to know. Just ask yourself if a sleeveless undershirt (sort of halfway between an undershirt and a tank top).

A few years ago, tallit katan makers started making various garments that are designed to be worn not as an undershirt, but as a t-shirt, i.e. a single layer. Most have snaps along the side, otherwise it wouldn't be considered a four-cornered garment. Now there are two types: one is made of cotton (like our TzitzShirt) and the other is made of a synthetic material (like our DryFit). Personally I think the TzitzShirt is more comfortable, whereas the DryFit doesn't absorb sweat, is more durable and is requires less laundering.

But keep in mind that cotton is considered preferable from a halachic standpoint.