Depends on the age of the wearer

A busty girl wearing a bikini top with her tits spilling out is perfect for me.

Both can be hot.

Tits and ass are generally better to look at in a bikini and the sight of the mid drift is also nice.

However a slightly too small one piece usually leads to an amazing camel toe which always stiffens my cock.

Wife in one piece rear view front view

Have more of her in other swimwear if people want to chat

They can both work for me

i would say bikini but dam no complaints about this!

Bikini all the way for me. Although thinking about how a wet bathingsuit needs to be taken off, mmm