First, I work backwards. Like if I know I am on a travel trip, I plan to shoot maybe 150-200 shots and depending on the days x shots per day on a particular size, I look at suitable sizes of SDXC cards to buy. If you look at A7 raw, it is at 25MB per file, or 40 photos every 1GB or about 40x240 or almost 9600 photos on a 256GB card. Question is, do you need so many photos even on a trip? 200 shots on a trip is already a lot per day, which will translate to 48 days.
Second, I look at options on Lazada and Qoo10. If I need 256GB as options, is it better to have 2x 128GB to reduce risk of losing everything on an important trip. Is it also cheaper to have 2x 128GB compared to a single 256GB.
Third, I look also at future use or upgrades. If I am going to be contented with A7, or will I move up to the A7III in a couple of years. It is said that the A7 writes at 35MB/s? I am not sure, you have to find out yourself. The Sandisk range is the Ultra (15-20MB/s), Extreme (60MB/s), Extreme Pro (90MB/s) and Extreme Pro UHS-II (260MB/s) writes. While the Samsung is stuck with the Pro series of 90MB/s, Evo (10-15MB/s) and Evo Plus (15-80MB/s). Samsung is very confusing personally and they do not have great SDXC (not micro SDXC) range compared to Sandisk.
If you want to save money, the Samsung Evo Plus 128GB and 256GB are selling for like $60 and $140 with coupons and deals on Qoo10. For me, Sandisk is the top brand for reliability (not that my Samsung Pro has any issues)