I originally placed the first order, but it's currently back in stock. The second model is available for pickup today at the store. I'm trying to understand the differences between them...
In short, the U offers a slight upgrade—more RAM, probably just for marketing—and a 2.5G connection. The gaming version is way better, handling many more packets per second.
They are quite alike, yet the AX86U offers slightly better specifications and includes a 2.5 Gb/s WAN port. The processor now has two additional cores, and the memory capacity is doubled to 1GB. @Levent Remember that even though some products may appear different due to regional availability, ASUS has previously done this. For instance, I own two ASUS RT-AC68 routers—one AC68R and another AC68U. The latter model was available online through retailers like Amazon, while the former was sold only in brick-and-mortar stores such as Best Buy. Internally, they are identical except for the model designation.
These devices operate similarly in practice, so pick the one that suits you best. I don’t have any background with ASUS models, but I’ve worked with TP-Link since the beginning.
The RT-AX86S is a more affordable version of the RT-AX86U. It features a dual-core processor instead of a quad-core, lacks a 2.5 Gbps interface, and has only 512 MB of RAM compared to 1 GB on the RT-AX86U. Both models use identical firmware.