Generally 2.4 will give you more distance and 5.0 will give you better speed. Distance will slow speed. You are only as fast as the slowest link which can also be the device.

@Oscar1952 

 

A few I can think of:

 

• Do you have SMART CONNECT enabled? (Don't think you do as you said you set up both bands)
• Interference? Test all devices at the same location.
• Hardware, what is the Network hardware? 802.11 device speeds would have different speeds on the same band.

 

Not known, how are you measuring the speed?

 

Interference can come from many places, bands crowded or electrical motors/devices, and well as wall construction if between device and router.

 

Sometimes, Network Security could even slow down some devices.

 

Devices do matter, for instance, model of the iPhone, newer ones have AX speed, older are possibly AC speed (802.11).

 

By the way, what router do you have? What settings did you set for each band, channel, width, security, etc.?