Right now. whitehouse.gov
Built at speed, I think it was put together in 6 weeks (!!), when the new Biden administration came in. For me it was one of the first examples I had seen that demonstrated the potential power of the Gutenberg editor and block based development.
I’ve always been an admirer of the agency involved 10up. They presented their approach in a WordCamp in 2021. They presented it very well and it was an excellent overview of how they created the site, with bonus example code (abstracted as the whitehouse.gov code is not open source for obvious reasons).