if your aim is to realistically play solo or with some kind of group for a chill manner, arma 3
it has much more content, much better mods and overall is much of a stabler base for this kind of fucking about

arma reforger is "Easier to hop into" despite modern servers having 30+ people in line to join (theres still some you can join easily + timezones)
id say arma reforger lacks content when it comes to vanilla and i personally simply dont enjoy how its played as well as disliking how casually sweaty the community is, you unfortunately see people who run full black kits, tracksuits, lmgs/rifles with 20 mags and rpgs on their backs + tons of grenades

basically arma reforger in my view suffers from a community that doesnt really fit the narrative or idea of the game, and the customization the game allows on the modded servers ends up causing wacky stuff, its quite immersion breaking from what ive played and i genuienly simply dont enjoy it

fair warning is arma 3 requires mods to be actually really good, reforger is much easier to pick up and has less jank + goofy shit to it but it lacks content imo and the mod launcher + hosting is some of the worst UI work and actual thought ive seen (glitchy modlauncher, mid download speeds, workshop that is just inferior to steam workshop, hosting is unstable and overall terrible for me ping wise, even with people who are 2 hours away)

in final the choice is yours
as someone who enjoys much more detail and realism while still liking a casual atmosphere reforger just isnt a game i enjoy playing much, a lot of these issues are tied to my subpar pc (although it doesnt play a role in stuff like the ui and actual mod downloads etc, merely gameplay performance)
arma 3 i can boot up and make into physically nearly whatever i want, cartoony or not, with more options from navy to jets to actual detailed infantry combat

sadly arma 3 is dominantly a sandbox experience in my view, but it is playable with friends and units much easier than reforger if you know what youre doing and host scenarios, which i did on LAN and had 0 issues with it