We received 2 of these as a handme downs when our babe was younger, and were impressed how soft the fabric was, even on the second go-around. Since then, we've purchased several more, and the union suit has become our uniform of choice for our 1+ year old. He struggles with eczema all-over, and the suit keeps him comfortable and cool. The colors are very cute, and we call the black one his "ninja suit"
Also, the simple design maintains good skin coverage so there's not much access when he feels like itching. Its also pretty easy for us to unsnap, do diaper changes and apply put lotion all over.

Size:
At 15 months, the 18 month size fits fine and is slightly baggy, so there's room to grow.
Going 1 size up has worked for us all along, even if I need to roll cuffs for a month or so.

The fabric does stretch out over the course of the day, since he's a wriggler and kicker.