Terry cloth for bath towels usually use four kinds of yarn size: 21s/2 or 21s/1 , 32s/2 and 16s/1 as loops/piles, and apply 21s/2 as warps, 21s/1 as wefts to weave terrycloth base.
In towels business, yarn count make no difference between quality of towels, considering use which yarn count to weave towels vary according to application purpose.
Theoretically speaking, more fine yarns and less twist means more soft and delicate, but too fine yarns can not bear too long loops considering durability of towels. One ply 16s is not the finest but is often use for the most luxurious terry towels, because it is the longest plushy spiral loops/piles of towels. Long loops endow towels with excellent absorbency of water and softness of touch.
Considering various intention of application, there are certain balance among softness, absorbency and durability.
Terry factory used to use 1ply 21s yarn as loops for terry cloth/fabric and terry velour, in these days many factories developing use 1/16s yarn in stead of 21s/1 yarn, considering 16s/1 has long plushy loops/piles can give us more luxury touch.
But in my own opinion, 21s/1 yarns is better for babies towels.
Check the photo of towel below, the top towel is with 32s/2 yarn loops finer than which of 21s/2 loops on the bottom , but it is a bit little less durable than 21s/2 yarns.
Considering cost, 32’s/2 is a bit higher than 21’s because of spinning process, and spiral 16s/1 is similar to 32s/2.
The photo of the towel bellow is with 16s/1 ring spun yarn loops. Because of long and spiral loops the towel seems fluffy and luxury. Towels use 16s/1 yarns usually is embellished with dobby border or cam border.