I think you should have him ask the kids he is closest friends with which system they have, and what games they play. The systems are comparable, so the "better" system is the one that will be easiest for him to play shared games with his friends.
Also brace yourself for saying no a lot because a lot of the common games that kids play starting in 5th or 6th grade are violent in some way.
He will be better off having whichever system the majority of his friends have if he wants to play with them. Generally Xbox seems more common with teenage boys. We have a PlayStation now, but will likely add an Xbox as my DS becomes a teenager.
I’m going to hazard a guess that his friends are probably playing what you would consider violent games though.
The games my 11 year old plays are probably not what you’d consider appropriate as they all have some violent content. He likes fortnite, Minecraft, Star Wars, and occasionally he plays things like Call of Duty or whatever.
We live in Seattle, where Xbox is definitely more popular. I would go with whatever's most popular with his friends.
V is 10, and at this point he just plays Minecraft and the Star Wars Kinect games.
I would just set some reasonable limits like X hours of "junk food" video games per week, or maybe you only get junk food games on Wednesdays and Saturdays, and after that it's Minecraft or whatever your threshhold for "not violent" is (Zelda? Mario? Mario Kart? Those are on the Switch but you get the idea). 12 year old boys will turn anything they can into a gun or poop joke, the important thing is to teach them there are times and places where that's not really okay.
Definitely ask about the specific games he wants to play and check for compatibility. Most of the new games are made for both systems.
The video game ratings are pretty good. There are definitely a lot of non-violent games out there (FIFA, Mario, the Lego games, Minecraft). Some have super-hero type violence. We have had to say no to Fortnite on multiple occasions, and there’s plenty out there that’s worse.
Xbox is definitely the system of choice here among DS (almost 10) and his friends. I agree about looking into what his friends have for compatibility reasons. My son got his last Christmas and we've had no complaints (other than, of course, having to limit his time on it, but that was to be expected).
We have both plus a switch. I think PlayStation has more kid friendly games than Xbox. Only my 13 year old son (and sometimes husband) play the Xbox. PlayStation has plenty of appropriate games for my 8 & 11 year old daughters. I rarely play anything, but when I’ve looked through the games available on whatever Xbox pass we have I don’t see many games appropriate for my younger kids. My son seems to have more friends with PlayStation, he’s one of the few with an Xbox.
We have both (and a switch too). We got an Xbox first and they still wanted a PlayStation. So we got a PlayStation and I think they play Xbox more because that is what we have for most of the sports games.
The only thing I will add is that the Xbox we have only takes digital codes and they're expensive as hell. PS5 games seem to go on sale more often.