So AC speeds are pretty confusing, but the higher the number the better the POTENTIAL speed. The only thing you really need to know is: unless you have a bad wifi connection (too far away/interference etc), your wifi will be many times faster than the internet.
Both AC1300 and 1900 have the same 1300Mbs max speed. In some cases. Other times AC1300 is ~867Mbs.
Don't forget to refer back to the first sentence frequently.
Check what your actual wifi connection speed is.
Where faster wifi helps is transferring large files around.
Even average 11n wifi will be much faster than very fast internet.