Hardwired is the best by far. Cat6 everywhere you can run it.
For home network WiFi, Ubiquit UniFi or Aruba InstantOn hardware has the best performance and security. Hardline run to each access point.
Next very good option is a mesh network, but be very careful about brands. The typical consumer brands often have severe vulnerabilities that may not get patched quickly. That's why brands like those above are far superior.
WiFi 6 / 802.11ax hardware is unnecessary unless most or all of your wireless devices support it. Even then, a high-quality device with good 5 GHz radios will outperform a cheap consumer-grade one with AX.
A range extender is the least good option, as it has the potential to slow down devices that access it. They are half-duplex devices. It's a band-aid that can help, but It's far better to actually fix the problem
Before you buy new hardware, you need to locate your router / access points where they can work their best. If you can locate them centrally on each floor, that's your best bet.
Instead of letting your router / AP automatically choose channels, set them manually. Use a WiFi scanner app (I recommend Ubiquiti Wifiman) to look at what 2.4 GHz and 5 GHz channels are being used nearby, and set your channels to less crowded places. If you have multiple APs, set them to use channels far away from each other.
Look at your antenna orientation. Mast antennas on WiFi devices are not omnidirectional; they radiate a toriodial (donut) pattern with the antenna poking up through the middle. If you have a device with multiple antennas, you can aim them in different directions at right angles to each other to strategically "aim" those toroids in different horizontal or vertical patterns.