I have a bucket of failed trials. So, it may take a few attempts to find what matches your body dimensions and likes. My experiences...
Sizing and material weight varies a lot. Take Onesies Downunder (ODU), they are lighter weight material, and run small and slim. Whereas, 4care are heavier weight (better for cold weather) and run truer to size with a more generous cut (waist). For instance, I have a 32" waist and wear a XXXL in ODU (slim cut fits perfect), and a XL in 4care (baggy waist). Check the size charts carefully before ordering.
Modesty and support - I choose/need to wear a onesie basically all day, everyday, and find the sleeveless (tank top) increases my freedom of movement and I stay cooler. A second benefit to the sleeveless is it reduces shoulder strain which in turn, helps with posture. I need them for work, business casual so, prints are cute but, not a good recipe.
Weather - In hot weather the ODU tank tops are great owning to the lighter material. The downside of ODU are the snaps. They will break over time. Repairing, there are four (?) snaps thus, you can get by with 2-ish broken ones. A snap-kit may repair the broken snaps but, I have yet to verify this will work.
Fashion - Intentionally, not a high degree of bling here. 4care comes in 4 basic colors. ODU sleeveless has a wider selection of solid colors. Looking for a bit of whimsical fun? Prints are only available with sleeves at least from ODU.
There are other suppliers as mentioned. I haven't tried them out but, others can attest to their qualify and fit. I would like to hear about Kin's durability if someone has experiences with them.