A crew neck is a classic choice, and this one does it right with soft stitching.
Chubbies The Relaxer Men’s Size Small Navy Blue Palm Graphic Sleeveless Tank Top
What makes this shirt comfortable is the round neck that doesn’t bind.
adidas Train Essentials Crew Neck Athletic Tank Top Mens Blue Casual Tops JC5372
What stands out about adidas here is the consistent quality.
New Look Mens Sleeveless Longer Tank Top Size Med NWOT Cotton heather blue
This one fits men who prefer a more athletic cut without being tight.
Fruit of the Loom Men’s Medium Navy Blue Sleeveless Crewneck Tank Top Basic Fit
What I like about Fruit of The Loom is how they keep things simple and reliable.