SD Cards are rugged and reliable. Simply, they are the storage device of choice for all dSLR/Mirrorless cameras with good reason. Here is a helpful guide for selecting the best SD memory card for portrait and wedding photographers.
How much memory do you need in your memory card?
First determine the average RAW file size from photos taken on your camera and establish how many photos you can fit in the SD cards on the market. Standard professional SD cards hold between 32 and 1,000 gigabytes, but there are even some SD cards on the market today can hold up to 2 Terabytes! These cards are unnecessary for portrait photographers and should be reserved only for those taking movies with their DSLR/Mirrorless cameras.
In lieu of purchasing one very large memory card for their photo sessions, most professional photographers like to purchase many smaller ones. When frantically photographing a wedding, there are just too many moving parts, and if your only large memory card is ruined, you will have a very angry bride at the end of the day. Because of this concern, you should determine how many photos you want to fit on each memory card.
I, personally, use 32 GB cards and shoot with a Canon EOS R camera for all of my weddings. This is a reasonable card size that holds approximately 900 RAW photos. I find it best to break up the wedding day with each memory card, and these 900 photos seem to fit nicely with the different stages of a typical wedding day (getting ready, ceremony, reception, and dancing). Simply, it is best to not have all of your eggs in one basket.
How much speed do you need?
Most professional portrait and wedding photographers tend to be more deliberate and careful with their shooting. This, then, generally does not necessitate the use of high-speed memory cards. There may be times when you fire off a few quick shots of your bride in succession, but the internal memory of your camera can usually store these files while the memory card is processing.
If you also use your camera for sports or live action photography, by all means purchase a high-speed SD card, but it is just not necessary for wedding and portrait photography. For those who just need to have top-of-the-line equipment, do not get a memory card that is faster than you camera can handle. For example, the output RAW size on my Canon is about 20mb and my camera can only shoot about 8 frames per second. Therefore, I should not get a card that can process faster than 160mb/s in writing speed, since my camera cannot even process that fast!
What brand should you purchase?
Really, this is somewhat irrelevant and may simply come down to brand loyalty. Most professional photographers seem to use SanDisk and Lexar SD cards, which both offer a full line of cards specifically catered to the pros. These cards are specifically built to withstand extreme temperatures and humidity, so they should be able to take the beating that you will undoubtedly give them. There are a number of very inexpensive off-brands on the market as well. They may work just fine, but you should use at your own risk.