They're close enough in games to where I'd take whatever is cheaper.

https://www.techpowerup.com/review/amd-ryzen-7-9800x3d/17.html

The 12400 is tested with DDR5 there, so it might be a bit behind with DDR4. It will probably be a bit faster outside games.

If you want to consider upgrade options offered by either platform...

LGA 1700 will allow Raptor Lake... in theory. But I wouldn't trust one given their known issues. Outside tech circles, the issues probably aren't known about, and your average person isn't going to be updating their BIOS. I've seen people with ones that have exhibited crashing issues (meaning they are degraded and unstable at stock) "solve" the issue by down-clocking them with XTU and then considering it "in working order" because they either can't be bothered to do an RMA, or refuse to believe it's faulty because they "got it working"). So I'd say that leaves "trustworthy" upgrade options as the 12600K, 12700K, and 12900K. And you'll still be on DDR4 with them.

AM4 will allow you for a 5700X3D or 5800X3D upgrade from the used market in some years when they are cheaper. That may or may not be worth it though. The 5800X3D is a bit better than the 12900K on average in games (and is worse outside games), and sometimes competes with 13th/14th generation CPUs (again, only in games). The 5700X3D will likely be the more worthwhile one and is probably closer to a 12700K/13600K or so.

If you have no future upgrade plans, flip a coin or take the cheaper one.

I do agree with what someone said earlier and would consider saving until you can get an entry level CPU for AM5. It will cost a little more, but in turn, it will be a little faster than the options you're looking at and will also have much more worthwhile upgrade options. You don't have to do this, and maybe you're saving two or three hundred not to do it, which would make the cheaper options you're looking at more viable. But usually the prices aren't that far apart.

Whatever you do, if you go with a DDR4 option, get 32 GB soon. DDR4 pricing isn't as good anymore, and it's not going to get better. If you find out you need more RAM later, it might end up being more costly. And then you compare 32 GB pricing, the AM5 route probably looks better.