IMO it's better single player, but then I don't like people. AFAIK there's little gameplay reason to multiplayer.

Be aware that there's no official servers, you either client-host or run your own dedicated server - there's also no anti-cheat, for anti-cheat you need mods even if all you want to do is ban all other mods. In short multiplayer in Valheim is designed for friend groups, not public servers.

Edit: serpents are slightly awkward single player, what I do is nearly finish them off then jump in the water and punch them so that their sinking drops instead land on me and get auto picked.