It's very much the same thing, there is no single unifying "Alt-Right" central headquarters, subscription fees amd newsletter, just as there is no specific Antifa organisation, just many people and a few groups that self identify as being against facism.

On the AltRight side people might point to, say, Steven Miller and his Nazi adjacent statements, or to Nick Fuentes and the Groypers, or to Andrew Anglin and The Daily Stormer for more trad. Nazi views.

To be honest I'm not entirely sure what the leading antifa groups in central north america might be.

In terms of the silliness / uselessness, you're right that they're similar - nobody compares "The alt-right" to the Red Cross, as if they had an office and an accountant on staff.

But plenty of people will say that they are traditional conservatives, and say "I'm not alt-right". Virtually nobody describes their own political views by saying "I'm not anti-fascist."