My 2 cents:

Simple, no domain required stuff:

• Pi-hole for self-hosted DNS: https://pi-hole.net/
• Navidrome for self-hosted music server: https://www.navidrome.org/ (best to pair this with an external portable HDD/SSD for music storage)
• Set up syncthing on it and use it for automatic file back-up: https://syncthing.net/ (that external HDD/SSD will come in handy again).

More advanced, should pair with a domain:

• Nextcloud for your own personal cloud/calendar/etc: https://nextcloud.com/ - it won't be blazing fast but it will work well, I had it running on a pi for a while.
• Simple web hosting - the pi is great for hosting low traffic stuff like blogs etc.

I am currently running

• Nextcloud: slow, but great for Calendar or Notes
• Gonic
• Airsonic Refix
• transfer.sh
• FileBrowser
• Conduit
• Cinny
• Mosquitto
• Prometheus
• Grafana

The last three are quite niche. I use Prometheus + Grafana for Monitoring the Pi itself and for displaying MQTT Stats. Since upgrading to SSDs performance is actually quite good, especially when taking power usage into account.

Jellyfin, I've run mine for a couple years now(ever since the pi4 came out) and it's been great. The only thing to consider is turning off video transcoding, its not able to to transcode anything HD or over. Other than that, its great. I use it for videos and music.

Best is so subjective.

I am running pivpn, pihole, all the arrs, jellyfin, gitea and rundeck.

I had jellyfin, arrs, wireguard and a lot more, but adding nextcloud was too much for 4GB. It would start with 2.7 GB used, but building until it OOMs. Also rpi cant transcode, but its perfect for direct play. I upgraded my server to PC version once I had to upgrade storage. Running multiple disks from rpi requires extra cables, devices and then its not cheap small factor anymore :)

Now I have raspberry for 2nd pihole, 2nd wireguard, duckdns, upsnap (WOL) and filebrowser

What do you want to use it for? Like software dev or something to host like next cloud or whatever?

https://github.com/marchah/pi-htpc-download-box this is great! I have a Plex server running on my shield pro

• Home Assistant
• Minecraft ( gotta go with something like PaperMC server but even core server will run if you setup a drive on USB
• PiHole (but as I commented elsewhere, it's overkill and you can use Pi Zero's for this easily).
• OctoPi (3d Printing)

Currently using portainer to run

• freshrss
• syncthing
• samba share While plugged into an external 3tb expansion drive. I want to do more but i only have a 2gb version so im afraid i might be pushing it.

It honeslty depends on what you do and want. I use syncthing instead of cloud services to bavk up everything i need and because i play emulated games a lot on both pc and my steam deck i can essentially have cloud saves for them.

The raspi is either a small hacking tool, or a learning tool. It certainly isn't ideal for things like nextcloud, but it is by far the coolest and most fun way to learn Linux and self hosted services. I ran emulation station, did nextcloud, pihole, pivpn, fail2ban, did robotics, learned python. I now use it for one thing - pivpn (Wireguard) and pihole to access my home network remotely

Immich, whoogle, syncthing, openmediavault

I have Adguard and Kavita on it.

Update: I forgot I have Wireguard too.

I have 3 rpi4 4gb doing job that I use practically every day.

Pi-1

• wireguard

Pi-2 portainer agent

• bedrock Minecraft server

Pi-3 portainer main running omv6

• Kavita - amazing comic book organiser and reader
• emby - Plex and jellyfish both crapped out, apparently due to library size corrupting the dB, emby is very nice though.
• homepage - nice homepage for everything
• paperless (5 containers!) - just installed document organiser
• metube - great yt-dl web wrapper

The pi4 especially is great for proof of concept or MVP testing, but I often migrate to VMs on my proxmox hypervisor once something becomes critical. I started Shinobi, pihole, and home assistant on a pi4.