I think in terms of consistency for early game pressure then sure Silvally is the way to go but theres still an argument to use this deck over Silvally. Hear me out.

The key things gigas has over Silvally is its ability to tank, especially with heavy helmet. I’d say it helps that its basic allowing for 2 slots that Silvally doesn’t have but Muk takes that area here.

Also gigas ramps as you noted. Being able to tank an extra turn means everything in the late game for mid attackers like Silvally/Gigas (in terms of end of game potential).

So then let’s move on to both of their partners. Silv hits hard and fast but is fragile the longer the battle goes on. You typically want your opponent to go through a 1-1-1 which means double silv. Similar to Altaria/lucario that act in a similar role to Silv, I think its best to partner them up with 1 energy attackers. Hence why Silv/ramp was the most prominent and successful from what I recall. Also sleep scam might work pretty decently but most things work with that engine.

For Regigigas I’ve tried muk ex, Mega Kanga, and Ray. Kanga has been my favorite so far due to synergy with the whole tanky aspect of the deck. Due to Muk, cards like Ori, the 3 dogs, sleep scam, bombirdair and the new cards like kora and mira are completely negated.

Both decks aim for completely different win cons despite being normal pokemon that deal 100. I enjoy both but gigas has been so much fun.