WiFi will allow you to connect to the router without having to connect a wire. There are different WiFi spots that you can find in public places, and this is also something that you can have right at your own home. Cellular data, on the other hand, will allow you to connect to the internet, but this will depend on your phone signal.
The higher the signal of your phone, the faster the data connection that you will get. There was a time when it was only 2G available, but the cellular data offered to people now is 5G. This is definitely faster than the type of data offered before. WiFi connection has also improved steadily over the past years.