@PhrmXD 

When configuring RE you can use this guide.

With this method your RE is connected wirelessly to your main router.

You could connect to the RE wired or wireless in this scenario.

When the RE is configured in AP mode you could connect to the RE only wirelessly, because its ethernet port is already used by the AP mode configuration.

With this method your RE is connected by wire to your main router.

Which mode you'll use depends on your infrastructure properties.

Also to know in which scenario you'll get a better speed to your computer, you'll have to test each of them.

Keep in mind that the RE ethernet port is 100 mbps.

Of course, the best speed you'll have is when your computer is wired direcly to your router.