MAC address filtering is a very weak form of wifi protection:
- the MAC addresses of your devices can be easily eavesdropped with tools like wireshark
the MAC addresses of their devices can be easily changed (OS dependent, but typically an option in Network Settings).
MAC address filtering is annoying to maintain. You have to login to your router configuration every time a new device connects, find the MAC address in the settings of the new device, type in 12 seemingly-random hexadecimal digits (or copy from the logs of connection attempts), and still tell the new device the new strong wifi password.
To secure your wifi, make sure you use WPA2 with a strong passphrase (e.g., 6-8 random words) with WPS (Wifi Protected Setup) disabled (WPS is broken). You should also check that your router doesn't have any known backdoors.
The strong high-entropy password is extremely important. Wifi passwords can be cracked in offline attacks after capturing a handshake, at a rate of trying millions to billions of passwords per second. However, 8 words randomly taken from a dictionary with 10000=104 words, means there are 1032 passwords the attacker would have to try (assuming the attacker knew that's how you choose passwords -- the rate will be worse if they don't know this). At a rate of a billion passwords per second per computer with a million computers, it would take more than a billion years to crack an 8 random word password. (Note picking a well known quote/phrase is much much weaker even if it is 8 words long.) A passphrase of six random words would have 1024 (e.g., with a million computers doing a billion passphrases per second it would take only 31 years to break). Note a four-word passphrase only has 1016 so a single computer doing a billion passphrases per second would take about a month or two to break it. A three-word passphrase can be broke by a single computer in under 20 minutes.
Note, if you choose to go the random characters route, if you choose characters randomly from uppercase+lowercase+numbers, then a three-word passphrase is about equal to a 7 character password, a four-word passphrase is about equal to a 9-character password, a six-word passphrase is about equal to a 13 character password, and a eight-word passphrase is about equal to an 18 character password.