Urshifu SS is most likely the best Gigantamax Pokemon you can use because like I said in the comments its a great wall breaker and has a slightly stronger signature move than Urshifu RS. Tho it isn't the best Pokemon to use in AG and isn't used much in that format, the benefits that Urshifu has can't be left unchecked because Its abilities make it super broken, which is why it is in Ubers, Assault Vest Urshifu can take out Calyrex SR, and can hit all the Necrozma forms hard. Choice band increases its power and wicked blow always results in a critical hit which is over powered. So based on all that, it's worth it but only if you actually need it on your team for Gen 8 AG and not because (its strong / really broken), there are more Gigantamax Pokemon that can fill it's Gigantamax role but most of them are not as viable in AG. here is an Urshifu set I made as an example, I really hope this helps answer your question.
GIGANTAMAX URSHIFU AG
Urshifu-Gmax @ Assault Vest / Choice Band
Ability: Unseen Fist
EVs: 4 HP / 252 Atk / 252 Spe
- Close Combat
- Wicked Blow
- Iron Head / Poison Jab
- Stone Edge / U-turn
Close Combat --> Max Knuckle
Wicked Blow --> G-Max One Blow
Iron Head --> Max Steelspike / Poison Jab --> Max Ooze
Stone Edge --> Max Rockfall / U-Turn --> Max Flutterby
- Close Combat strong STAB and hits Dark-resistant foes mainly like Yveltal on the switch.
- Wicked Blow STAB and always results in a critical hit and it ignores protect and detect thanks to the ability Unseen Fist. When Gigantamaxed, Wicked Blow turns into "G-Max One Blow" and breaks through Max Guard and any protect like move.
- Iron Head / Poison Jab both hit fairy types while Iron Head has a good 30% chance to cause the opposing Pokemon to flinch and Poison Jab has a good 30% chance to cause the opposing Pokemon to be poisoned.
- Stone Edge is strong coverage that hits Flying Type Pokemon.
- U-turn to pivot out of bad spots and to get other teammates in safely.
Ive also posted this set as an answer on "what's a good move set for Urshifu" btw. Here is the website where I got the Gigantamax form from, it has all the other Pokemon sprites as well including mega forms.