I do buy Swimwear online and I mostly buy my Swimwear and most other clothing through Zulily who has great products as well as fast shipping and great prices.
I don't buy Swimwear often but when I do I either buy it through Zulily or even Amazon or ebay as it depends on what brands and styles of swimwear I'm looking for.
Buying swimwear in stores offline is also good because you can see it in person but you do get great deals online for most swimwear and other clothing.
I also buy swimming toys for my kids and lounge chairs etc online as well because doing so is much cheaper and I prefer shopping from the comfort of my own home.