Least sketchy? Haveno[2] is one of the exchanges that the getmonero.org site recommends. However, the platform with the most "institutional support" (if that's what you meant by least sketchy) that allows you to buy XMR is probably Kraken[2], but IIRC they have KYC that takes a few days before you can buy.

[1]: https://haveno.exchange/

[2]: https://www.kraken.com/