I had a Switch for a few years before the Steamdeck came out. If all the games you want to play are available to play on Steamdeck, stick with Steamdeck. It’s more powerful, has way more games, you probably already have plenty of games to play on it, the games are way cheaper, and the degree which you can modify the software and hardware is pretty unique for a “console.”
The Switch has an edge in form factor and is more convenient for me to use. Although Switch emulation on the Steamdeck is pretty decent, I still prefer the original hardware to play Animal Crossing or Zelda.