MicroSD memory card
If it is possible to install an SD card in your mobile, it is actually possible to install a microSD card. Standard SD cards are very large. In general, it is always best to buy microSD cards. And, it is possible to convert a microSD card into an SD with an adapter, but it is not possible the other way around. Therefore, the ideal is that always buy a microSD card. Thus, it will be useful for your smartphone, and also if you have a reflex camera.
Also, you should buy an SD memory card that is at least Class 10. There are also Class 4 ones. Nowadays it is possible to buy a Class 10 memory card for very little money, so buying a Class 4 card does not make any sense, in addition to being of poorer quality.
16, 32, 64 or 128 GB
What should be the capacity of the memory card? Nowadays it doesn’t make much sense to buy a 16GB memory card. And it is that for not much more money it is possible buy a 32GB memory card. It will cost a bit more to buy a 64GB memory card.
Ideally, you should buy a 2 TB SD memory card. However, many entry-level mobiles only support SD memory cards up to 32GB.
Usually, 128GB memory cards are significantly more expensive than 64GB. Therefore, my recommendation if you have a mobile from high-end is to buy a card 64 GB. If you have a mobile from mid-range, it is also a good option to buy a memory card of 64 GB. If you have an entry-level smartphone, the ideal is probably to buy a memory card of 32 GB. It is somewhat cheaper.
Samsung, SanDisk …
Now, what brand of memory cards should you buy? If I buy a Samsung is it better than if I buy a SanDisk? The read and write speed of the cards is what determines the price difference. The faster cards are more expensive. In this case, I think that a good option for a smartphone is a card with a writing speed of 20 MB / s. From here, almost all memory cards will have similar prices.