Any MFi cable is required to meet the specs Apple has determined, the main spec being 2.4amp @ 5volt. The problem is determining if the cable is really MFi certified or not. Note how
this cable doesn't say MFi certified and they advertise 2.1 amp.
https://support.apple.com/en-us/HT204566
Anker (or any name brand) MFi cable is a good choice because they wouldn't be able to falsely claim MFi certification for very long. AmazonBasic cables are also MFi certified and I've had very good luck with them although not as durable as the Anker cables.
iPad charging 2.4amp @ 5volt which is as fast as it will charge using an AmazonBasic 3 ft cable.
Its best to get a cable that is the minimal length you need. At 5v and potentially 2.4amp the conductors diameter (wire gauge) needs to increase as length increases to minimize resistance. As the resistance increases the voltage will drop. Devices with even the dumbest charging circuitry will decrease current to maintain voltage. Volts x Amps = watts so reducing volts and/or current reduces wattage and increases the charging time.
Like for like, longer is worse. Here is a quick example.
Using this hodgepodge setup of a UM34C USB tester with a LM25(?) simulated load to test a cheap 6 inch USB A to USB C cable vs a higher quality 6 foot USB A to USB C cable.
Having the load set to 1.5amp.
The 6 inch cable...
7.24 watt
The 6 foot cable
6.92 watt
Reducing the load to increase the voltage back to 4.85vdc with the 6 foot cable.
4.67 watt
Needless to say getting needless long Lightning cables is not only more expensive but will typically have less performance.
Try to glance at the lightning connector before inserting it into an iPhone/iPad. If you see a burnt or corroded contact (black or green) or you see the conductors exposed at any point of it just toss the cable. You do not want to put that into the phone because a poor connection causes high resistance and thus heat. That heat will damage the pins inside the phone just like the connector is damaged on the cable. You can use 99% isopropyl alcohol on a cleaning patch/cloth to clean the port, don't stick anything electronically conductive into the port (I use a slightly modified spudger from iFixit).
Hope this helps.