What are the indicators of good quality in printed t-shirts?

I've ordered two printed T-shirts from an online retailer, but I need clarification on which is better quality because they both feel the same.

Why do you need that clarification? What are your goals? And how do you personally define quality?

Differences in quality can come from the fiber, fabric and manufacturing.

Are they 100% cotton or blend with polyester? 100% cotton with longer fiber will make clothes more durable while shorter fiber or blended one will pill and wear out faster.
Lower quality knit fabric may be twisted.
Dye fasteness. Low quality fabric will bleed and the color will fade sooner.
Are all the seams finished neat inside? Are the hems even? Any reinforcing on neckline and shoulder seams?
How does the print feel? Some may feel stiff and crack after awhile.

May Lotito wrote:Are they 100% cotton or blend with polyester? 100% cotton with longer fiber will make clothes more durable while shorter fiber or blended one will pill and wear out faster.

This is an example of why I thought the OP should define quality. I won't personally wear poly-blends, but the wrinkle-resistance matters to some people more than the feel or durability.

I am assuming solid color knit T shirt with printed custom logo. Maybe it's something else.
Personally I am not against poly, it can give the fabric many desirable characteristics: color fastness, durability, insulation, wicking power etc. The problem is in some cooton poly blend, manufacturer will use lower quality cotton fiber compared to 100% cotton one.

Welcome Andrew!

Quality, in a sense, is in the eye of the beholder.

I look for natural fibers (I try to limit my microplastic emitting, synthetic fibers shed in the cleaning process) and I look for quality stiching.

I wear my clothes hard and need them to stand up! I have had good luck with Carhartt as I work in a paper mill and need something that can stand steam/oil/resins/dust and who knows what else.

One year just before Christmas, I got a flyer in the mail for some really cute printed T-shirts. I thought the idea was really clever and that my daughter and son-in-law would love them for Christmas.

When I received the T-shirts the ink was so smelly that I wished I had not spent my good money on those T-shirts.

I folded the T-shirts up, sealed them in Ziplock bags, and gave them as gifts with the explanation that I hoped the smell would wash out.

I never saw the T-shirts again and they probably went in the trash.

It is the thought that counts, right?

Never again will I buy printed T-shirts from an online source.

My suggestion would be to know the source or at least look for online reviews.

Without seeing the T-shirts in person what are the indication of good quality?

We have purchased a bunch of shirts from https://www.lifeisgood.com/tees/ -- there are many shirts with themes and messages that Permies might like, and more importantly, they are about the softest T-shirts you can find. HOWEVER -- the printing has typically worn off quite badly after about two years of regular wear, which I've never seen from another vendor. So again, depending on what you value personally, they might be worth checking out, but know the printing is temporary.

I always buy them used at thrift stores so can see how well they are wearing after others have washed them repeatedly
I avoid printed ones though unless they are something really cool but even then the print has to feel soft and wear well.

Like the 'car talk' guys say always buy used so it's apparent how it's aging.

The last time I was in a position like you are, I called the textile profs at a major university.  I got a straight answer, and, as I suspected would happen, the prof turned it into a class project.

#2 son wears a T-shirt all the time - under a dress shirt for work, or just plain for not work.

However, he only wears one colour (light grey) and no logos - I'll just say he's unique and leave it at that...

However, one lot we bought at a usually reliable store had spandex or similar in it, and they didn't last well at all. Also, straight cotton can be burned or composted, whereas once it's mixed with non-natural fibers, I'm limited to sending it to the dump. So when he needed more, we started researching our options.

One of the reputable brands on the web actually gave you the "pounds weight" (for a specific volume if I recall correctly). We bought some of the "6 lbs" shirts, and they're sturdy and seem to be lasting well. I don't remember the brand, but I could ask.

I have a friend who swears by the brand Gildan and looks for them second hand.

Like Anne Millar identified, some of the printed shirts have a smell to them that would drive me batty - some stores that specialize in them, the smell is so overwhelming that I can't walk into them at all. I'm pretty sure one of the smells is formaldehyde which I'm pretty sure I'm sensitive to, but regardless, I can't believe they're healthy for my body, so I'm not going there! Some fabric stores have the same effect on me, so I always wash fabric and put it in my shrinking machine (other people call it a "dryer", but I only use it for shrinking things...) before cutting it.

Jay Angler wrote: Also, straight cotton can be burned or composted, whereas once it's mixed with non-natural fibers, I'm limited to sending it to the dump.

About that, I have the impression that (some?) 100% cotton T-shirts use polyester thread in the serged seams. But I just went googling for that and didn't find an answer. Anyone know?

Christopher Weeks wrote:About that, I have the impression that (some?) 100% cotton T-shirts use polyester thread in the serged seams. But I just went googling for that and didn't find an answer. Anyone know?

I would say that the majority do, as I recall reading that polyester thread is easier on the sewing machines than cotton thread is.
Some people cut the seams out before composting. Some people, particularly if they believe in sieving their compost before use, remove it at the sieving stage.
We can get used, supposedly organic, coffee sacks from a local "fair trade" business. Most of the strings holding the sacks closed are not biodegradable and once I learned that, I did my best to make sure they were removed before use.

You will see a lot of clothing that says, "100% cotton exclusive of trim" - serging is considered "trim"! However, many places leave off the "exclusive..." and just like with organic food products, there's a minimum amount that doesn't have to be organic, which often is things like spices which can be difficult to prove well enough.