I’m guessing but since you need a wifi adapter, I’m sensing your computers don’t have wifi built in, which means they are probably somewhat old....
The single best thing you can do to upgrade an older computer you want to keep it, is add memory to it, it’s probably really cheap and will add to performance...
On the wifi adapter, getting data back and forth from the internet faster won’t do you any good if your computer can’t keep up...
Go with the 300mb adapter, it’s probably cheaper and you won’t know the difference....
If you had a state of the art laptop or desktop machine for 2021, then the fastest adapter might be a better solution, but my philosophy is don’t spend good money on old equipment...
I just replaced my laptop, the old one was nearly 10 years old, it had built in wifi but the keyboard was starting to lose keys, the HDMI port went bad, etc...
I had replaced the keyboard with a USB keyboard for $20 and it worked fine for a couple of years.....
My son just built himself a gaming desktop in October is 2019, and the motherboard didn't have WiFi built in. So we bought a little USB WiFi unit for it. Some are just built that way. We just ran Ethernet to his room a couple of weeks ago. He's much happier now.