When I started my personal instance, one of my goals was to run it cheaply and with little maintenance. Being writing Ruby for many years of my past life, the decision between Mastodon (Rails) and Pleroma (Elixir) was quite easy. A week later, my Pleroma instance is taking 500 megabytes of RAM and a few percent of the CPU of the second cheapest Hetzner instance (4.5€/month).
Even better would be a deployable binary service. Calling out all Go and Rust developers!
Written in Go. Not done yet. https://github.com/superseriousbusiness/gotosocial