For my 5d3 / 5d4 I always used Sandisc cards...
When I got the R5 I switched to Sony Tough, and then when I got a second R5 I picked up an Angelbird card.
The Angelbird card had twice the capacity (512 vs 256,) for close to half the price!!
The Sony is NOT worth the extra money - It gave me a little trouble, but the Angelbird
has been great. Highly recommend!
Angel bird is a great company, with great support.
They may not be as well known as some companies,
but it is easy to see they care about their products -
I have already ordered another 2 Angelbird CFExpress Cards,
and an Angelbird reader (I picked up a Sandisc reader with the first Sony Card)