4
I was hesitant because there were no photo reviews, I may be one of the first buys tbh but I figured the dress portion can be adjusted anyway so I can be sure that will at least fit. I was right, with the dress the arms are a little snug but not stiff or uncomfortable. It does not drop as low as the listing photos but if you get a bigger size to get that effect you run the risk of it being saggy around the waist and chest. The part I really hate is the bra/top. I feared it would come over padded but instead it came flat and wide as ever. Not sure whose bikini this would be but not my A cup. It also does not adjust to made the width less, it only stretches right back out. So note that.
Other than that cute, just adjust the bottom strings to whatever length and size preference. Im usually a 4 for tight fits, 6/8 for looser. I was thinking a M but ended up getting a S and I am glad I did. Quick, arrived in 12 days