I'm ready to expand my storage and was wondering about the pros and cons of getting two 32s or one 64. I'm inclined to get one 64Gb sd card because that seems easier, but then I'm wondering if having two 32s might give me some extra flexibility. Any thoughts?

If you have one card and it fails, you lose everything.

2 cards mean a failure doesn’t cost you all your footage.

Unless you plan on shooting > 32GB of footage in one go without dumping the card to your computer, 2 x 32GB gives you better redundancy and back up than a single card.

I have multiple cards 64, 2-32, 2-16  and the original Mavic Sd card. More is better.

I still have the original 16GB that came with my MP so I also got a 64GB.  Either way I just move the files off after flying anyway and never have to worry about running out of space.  I assume you still have your 16GB so I would get the 64GB.  Just do not let it make you lazy and not copy down the images after flying.  

A store close to me had a 2 pack of 64GB on sale so I grabbed that immediately. The more the better.

It's a case of considering flight time and if you want to switch SD cards between flights with the battery,- SanDisk Extreme microSD Card 32GB. With write speeds of up to 60MB/s, this card supports 4K 60 fps video recording at 100 Mbps for up to 40 minutes. It would be 80 minutes of 4k for a 64gb card.  If you have a 64gb and 4 batteries for a Mavic Air or Pro you would need 2 cards 0r 4 32gb with an SD card switch with each battery. The 4 cards reduces the risk of footage loss if a card fails or are unfortunate enough to lose your drone.  The other thing to bear in mind is that 2 x 32gb micro sd cards are usually slightly cheaper than a single 64gb..

I keep a total of 4 SD Cards in my case, along with one in the quad, and one in my phone.  For me, the redundancy and preparedness is everything.  This comes from being on weekend long excursions with my camera and not uploading pictures for many days at a time.  

Basically have 2 extra sets of cards with me, so that i can change the SD card in my phone as well as the Mavic at the same time.  That way i maintain the captured footage from the drone and the any local record that may have happened on the phone.   Most times, when i upload, i end up dumping the footage from the phone but occasionally, it has come in handy.

Celsus Posted at 2018-5-11 21:14
It's a case of considering flight time and if you want to switch SD cards between flights with the battery,- SanDisk Extreme microSD Card 32GB. With write speeds of up to 60MB/s, this card supports 4K 60 fps video recording at 100 Mbps for up to 40 minutes. It would be 80 minutes of 4k for a 64gb card.  If you have a 64gb and 4 batteries for a Mavic Air or Pro you would need 2 cards 0r 4 32gb with an SD card switch with each battery. The 4 cards reduces the risk of footage loss if a card fails or are unfortunate enough to lose your drone.  The other thing to bear in mind is that 2 x 32gb micro sd cards are usually slightly cheaper than a single 64gb..

I am looking for the best card I can purchase, got ripped off with 128 GB sandisk bought on amazon, mind you they will return my money however I would like to know which card would be the very best for my MP, I intend on filming in 4k

I have a good quality 64g card in each of my drones plus have 2 spares.  Having a spare for each would be overkill and expensive.