Black Hat is a pretty commercial conference, tickets for two days cost more than 2000$, if you want to attend the briefings. There are also trainings, costs vary and are much higher. The content qualitiy is usually very high, the attendees vary from consultants, CISOs, developers, and all kind of IT security professionals. There is a big crowd with about 17000 attendees in 2017.
The briefings are picked by a review board in a call for papers process. Researchers present their top work, often campaigned weeks before the conference.
In the business halls all kind of vendors are present and giving away loads of swag for attendees and also throwing parties.
Black Hat USA 2019 Keynote: Every Security Team is a Software Team Now by Dino Dai Zovi
I am mainly at the Black Hat for the Arsenal. It is a great opportunity for developers to present their work at booths that are also located at the business hall. For the last three years I could thankfully present AVET (AntiVirus Evasion Tool), which is giving presenters a briefings pass. The tools are also picked by a review board.
Defcon is the “real” hacker event in Vegas and is completly different as Black Hat (although both have the same founder). Black Hat and Defcon overlap one day, Defcon is four days. Costs for 2019 were 300$, qualitiy of the talks is also high and more fun might be included (like talks about phreaking). More offensive security stuff seems to be included here.
This year the event was spread over four hotels including four presentation tracks, several villages (areas with talks and hands-on for several topics), parties, CTFs, movies and so on. It was said that about 30000 people attended defcon in 2019, so everything was pretty crowded and also a bit confusing. Walking between the different spots can take between 10-20 minutes.
Defcon is meant to be a hacker con, which is true. Also, there is a strong drinking culture present, fist time speakers must drink a shot (and attendees demand it loudly).
There is also a media server which is worth a look.
If you have the chance to attend Black Hat/Defcon you should give it a try. It is great to connect and develop your skills and I have met some great people and made new friends.
For people who want to advance their career it is definetly great, but if it is your first conference you might consider to go to a smaller event. The atmosphere in Las Vegas is somewhat special, with the hotels, the casinos and the tourists around.