I use Notion for everything. I even made part of my notes public:
https://www.notion.so/Public-Space-for-Krzysztof-Kowalczyk-5...I love it.
Coda is still in closed beta. I requested an invite months ago and still didn't get it. It also seems like their focus is on companies/teams. Notion also supports teams but works just as well for an individual (that's how I use it).
Notion is only superficially similar to AirTable in that Notion is a mostly a note-taker with additional capabilities, including some that can do some of the things that AirTable does (i.e. building mini-spreadsheets/databases).
AirTable is mostly for creating database/spreadsheet applications. It's great for that but not at all suitable for things that Notion is great at i.e. note taking.
I wouldn't even consider them competing. Maybe at some point Notion's tables will have as many features as AirTable but that's not today. You can use them both.
