I'm clearly biased since I work at Datadog[1], but I use and recommend Cloudcraft[2] for diagramming. As I don't use the cloud I focus more on the manual design tools, but the automatic stuff are pretty neat.
Recently, though, I've been using D2[3] a lot and really liking it. The diagrams don't look as aesthetically pleasing to my eyes, but being able to design everything with a simple language is pretty cool, and helps with automation.
[1]: Datadog owns Cloudcraft, hence the bias. Plus, I work in the Cloudcraft team, haha.
[2]: https://www.cloudcraft.co
[3]: https://d2lang.com
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