So the speed shown on the box is the total added up speed and now what you're going to get.
Essentially 500mbps@2.4ghz + 1000mbps@5ghz for 1500AC
If its tri band then it's something along the lines of 500mbps@2.4ghz + 1000mbps@5ghz + 1000mbps@5ghz for 2500AC
The signals they uses are going to be N, AC(wifi 5), and AX(wifi 6)
For the most part recommend AC since it came out in 2013 unless they need the best of the best, in which an expensive AX router would be better.
N is very very old and most routers are backwards compatible so unless they have the worlds worst budget don't recommend.
2.4ghz wifi is slow but can reach a whole house with a stutter filled connection
5ghz is fast but can't go past 2 walls
mu-mimo is dead and it's tech was reincorporated in AX, these work better in mesh networks because of that.
I love using Ethernet, I find that it is slightly faster than WiFi, and it has less interference then a standard Wifi connection. If you are considering switching, I would definitely recommend it.