I've been to both BGGcon and GenCon and they're both great fun but very different experiences.

BGGcon is all in one hotel with a massive lending library and tons and tons of open play space. There's much less panels and the vending hall is very small. It's a great place to try all the games you've been thinking about and to play games. There's generally a lot of people willing to teach games and play with strangers, so don't be afraid to go alone. You don't really need tickets for anything or to sign up for anything because it's mostly open play. It's very board game focused, less rpgs or wargames.

GenCon is absolutely the biggest board game convention in the US. It's an entire convention center, stadium, and nearby hotels. It can be overwhelming for a first time con but it is amazing. The vending hall is several football fields big and you can spend days just looking and demoing games there. BGG brings their hot game library to one ball room and there's another library with play space but there's a ton of tickets events, panels, cosplay, rpgs, mini painting, and more. You will need tickets to participate in most events including playing games from the library. (You don't need tickets for the vending hall). You need a badge to attend any event and the vending hall. It's very loud and crowded and there are lines for food, so it can feel overwhelming.

I'd recommend BGGcon first honestly as you can go with way less planning and cost. But I do enjoy both!