I'd go with Sun just because of more pokés, but you might hate Z-moves. I despise Tapu and Ultra Beast not being categorized as 'special' and banned from the 'Special Pokémon: Banned' list. One thing I did like, no more need for multiple HM-only 'mon. You can literally set Fly, Surf, etc, to a direction input.
One thing I REALLY didn't like about OR/AS was having people automatically join on your 3DS friends list, as in: you use GTS, the person who trades with you becomes your 'acquaintance' and gets their FC registered to your friends. Automatically. Maybe there's an option to stop it, but I literally have no desire to keep trading in OR/AS. I do like the Player Search System more than festival plaza.
So for someone who doesn't care about Mega Stones, you'll be fine. If you ever heard of horde battles, Sun has a mildly annoying revision of it: SOS battle. There's an added feature that lets you photograph 'mon, but don't think Pokémon Snap. If you like bikes, multiple fishing rods, safari anything, gym battles, or not having to press 'A' to walk in buildings, your nostalgia will be decreased.
The music in Sun is good, the graphics look pretty good (better with outlines off), the story is nothing mind blowing, but there are many 'questionable' things people say which are hilarious if you've got a dirty mind. Battle Royal is a strategic style of fighting, but I miss triple battles.
I don't know your limitations, but if you can get both, get OR first, then come back to Sun when things have been 'fixed.' If you only want one, go with Sun, but know that Lunala is better than Solagaleo. Even the card of Lunala is better than the card of Solagaleo.
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Well, you got my future point in the past. Good stuff.