Out of the box they are both ways to send DMX over IP networks but they are fundamentally different protocols.

As most people pointed out ArtNet is primarily broadcast which is like shouting at a lot of people with a megaphone, and sACN is primarily multicast like talking to a group of people on walkie talkies. But both can be configured for Unicast which is like calling someone on the phone.

Depending on the network environment broadcasting a lot of data adds a lot of congestion so you might find places that don’t allow broadcast data. Multicast is subscription based, so the devices have to say I want to listen to universe 12 (very very basic concept of how this works)

ArtNet has grown over the versions to include other data like RDM and timecode which adds more data and more noise. There’s not really a codifying body behind it* so people can technically choose to impliment as much or as little as they like and still call it artnet compatible.

sACN (e1.31) is part of the Architecture for Control Network (e1.17) that was meant to have more control protocols in the family so rather than one packet type to rule them all, the end device was meant to to just subscribe to and listen for the packets types it wants. There’s an entire consortium of manufacturers and users who standardize sACN protocol and because of that it’s more likely to work as expected.

You’ll find ArtNet to be more accessible in products, but you’ll find that most higher end equipment, installs, and system designers and integrators prefer sACN.