Mine is Pokemon HGSS (the amount of content is mindboggling), Pokemon Platinum (grandest Pokemon experience) and Pokemon Black 2/White 2 (most fun and unique playthrough). I’m also looking forward to buying Legends: Arceus on the Switch, have heard many great things about it!
Hey Pokemon Ruby is my first game too! Definitely my hook into Pokemon, though arguably Emerald has a lot more content, Ruby will always hold a special place in my heart