Same for me, except I've started buying Brooks Brothers underwear. It seems to hold up much better than the Kmart.I never did before my military service. Since then I always wear an undershirt (except with fine gauge polo shirts that tends to "stick" to the undershirt).
The armpits of my shirts look just like the rest of the shirt! Maybe I'm lucky in that I don't sweat unless in the midst of extreme physical output (to the point that I don't wear underarm deodorant or antiperspirant). I think those are what make the fabric of your underarm discolour.You're going to ruin those nice dress shirts sooner rather than later if you go sans-undershirt. Just look at what happens to the armpits of your undershirts... yellow within a month or two.
I, and presumably the others who made similar claims, don't sweat to that extent where it discolours the arm pits of our shirts.Always wear an undershirt with dress shirt. Crew neck if the dress shirt is buttoned, v-neck if it is unbuttoned. The undershirt keeps sweat and skin oils away from the dress shirt. Those of you who claim not to sweat should probably consult a doctor.
At the moment my favorite is Jockey Classic. Not expensive, but not the cheapest at $16.50 3-pack. Fits me well, seems to hold its shape better, shrink less than others I've tried (so far).Same for me, except I've started buying Brooks Brothers underwear. It seems to hold up much better than the Kmart.