I had a GX470 for several years and just recently got an '04 4R V8. I think both are fantastic, and you can't go wrong with either.
If you get a GX, plan to replace the rear air suspension + electronically-controlled shocks, either when the air springs fail or for a lift. No air suspension on 4R.
Much easier to find a non-nav 4R than GX. If you read this forum, gxor, and IG, you know that the GX nav caused COVID, may contribute to mental disorders, and just generally makes the vehicle undriveable (rolls eyes). Point is, it's much easier to upgrade sound system in a non-nav, and non-nav 4R's are more plentiful. (I am one of the freaks who loved the ML system in the GX.)
The 4R has much more usable storage + bins up front than the GX, and bona fide cup holders. However, the ergonomics of the 4R fall short of the GX, such as the window/door switches on the driver's door. And the lack of theater lighting in the 4R, which the GX has, makes it hard at night to find the right button. O and the 4R front map lights do not come on when opening the door, this requires a quick/easy mod to fix.
The 4R 2nd row, as noted previously, fold up much more elegantly than the GX and you get a flat surface. I'm 5' 11" and can easily lie down.
Subjectively, I find the GX body has aged beautifully, a timeless design and every time I see one I smile. The 4R looks great from every angle that does not include the front end.
Just find either one that has maintenance records and has been cared for, that's most important. There are +/- to both, but in the end they are nits really since it's the same platform.