Did you ever wonder why you experience different internet speed's on two diffrent devices, even though placed in the same location and connected to same wifi router?
Well the answer could be diffrence between number of antennas in each device. One device could be using 1×1 or 2×2 MIMO, whereas the other device with higher internet speed might be on 4×4 MIMO. The device with higher number of antennas the higher will be the data transfer, so will be the download and upload speed.
LET'S MAKE IT SIMPLE:
Think of MIMO as highway lanes. If you have a highway with 6 lanes, it allows more traffic as compared to four or two lane highway.
Look for MIMO in connectivity specifications and add #1morefilter while comparing devices and making buying decision.
P.S.:Though the MIMO applies for both WIFI and cellular network, the antennas used are different.