go check here :
https://ripple.com/xrp/buy-xrp/

if you want to know where is the place that you can buy XRP using USD,
every exchanges have their own weakness and their own advantages.
for example Kraken,
their biggest weakness or problem is their website,
you can not make an action when the market move,because it will lead you to an error page.
but they did not do a shitty thing like others.