I am several months into the self-hosting journey and I feel I have outgrown my Pi 4 B 8GB. I'm only running around 3 dozen containerized services and it seems to struggle to keep up. But I'm not sure of the best bang for my buck. I'd like good, long-term performance, but I don't really have a grand lying around for a Lenovo Tiny or Dell Optiplex or ASUS NUC. I'm thinking of buying an SSD to boot from, but will this even help much? For $350-500, could I make a more cost effective homeserver upgrade?
For me, the small energy footprint of an ARM machine is really important for home usage so I personally went on multiple occasions with Odroid’s offerings and as long as you have a tinkerer’s soul, I can really recommend it.
In that case, I can recommend minicomputer's like HP EliteDesk G2 800 Mini. You can get them with a variety of intel CPUs, they can take up to 32GB RAM, they have slot for M.2 disks and a regular 2.5" SSD – and they hardly use any power when idle, between 5 to 10 watts, depending on the CPU and CPU governor settings. They are sold used for ~€50 and if you buy newer generations you'll get even more umpfh for a bit more cash.
In other words, very competetive with the Pi's, only more available, cheaper and about the same power consumption!
Intel's low power offerings are sometimes even less power hungry than a RPi and handle more stuff. I like Asrock's line of CPU-onboard motherboards and use one myself. You get the convenience of a full x86 machine but it sips power. Mine peaks at ~36W with full load on CPU, GPU, RAM and 4 SSDs or disks. Usually it is much much lower. You can always go smaller with an Atom x5 z8300 (~2W Idle without disks or network, 6W with both and some load), but those are getting a little old and newer stuff is better and more feature-rich. Maybe an N100 machine with 4 or 8 gigs of RAM are a good option for you? Don't go overboard with RAM if you are using docker for everything anyways. I use 8 but 4 would be more than enough for me and my countless containers. I run Nextcloud, Jellyfin, Paperless-ngx, Resilio, Photoprism and a few more. Only the minecraft server benefits from more than four. Very happy with my J5005 board.