We're a virtual company made up of tech experts from across the globe. We love the Raspberry Pi because it was designed as a learning tool, and it works well for hobbyists due to its low price and extensive support. We also love them for the fact that they're easy to set up.
SanDisk is the king of flash storage, and its 32GB Ultra card is the best bang for your buck if you're picking up a Raspberry Pi. You likely won't need more storage than this, but if you need more, SanDisk and others offer cards with higher capacities.
The SD card for you
SanDisk Ultra 32GB
32GB is plenty for the whatever OS you install on the Raspberry Pi, with some space left over for games, programming environments, and whatever else you want to keep installed. If you intend to install a lot of games though, you may be better served with a higher capacity card.
A similar card
Samsung EVO Plus 32GB
If for some reason SanDisk's card isn't available, this one from Samsung is only a bit more. It'll be more than fast enough for your Raspberry Pi, and it offers plenty of space for you to tinker.
Samsung EVO Plus 64GB
If you're going to use your Raspberry Pi for gaming or as a desktop computer, more space is always better. This 64GB card is just as fast as the previous one, so it won't slow your Raspberry Pi down. And it's only a few dollars more than the 32GB version, but with twice the storage.
Whole lotta space
SanDisk Ultra 64GB
If you're going to use the Raspberry Pi as a desktop computer or as a game console, you'll need as much space as you can get for programs and games. This 64GB card is only a little more expensive than the 32GB option but offers twice as much storage.
Less storage, lower price
SanDisk Ultra 16GB
If your Raspberry Pi is being built for one specific application — as a print server, VPN, or another similar task — a 16GB card will be enough space for you. This one from SanDisk is just as fast and reliable as the higher tier models, just with less space.
Kingston Canvas Select 16GB
16GB is still a lot of space, depending on exactly what you're using it for. If you need the bare minimum amount of storage for your Raspberry Pi and don't want to spend any more money than you have to, this is the card for you.
32GB isn't a lot for our phones, but it's more than plentiful for the Raspberry Pi 3 B+. You'll easily have enough space to use the Raspberry Pi as a print server, a VPN, media center or even as a full desktop — so long as you only need basic programs. You CAN get a bigger card — or a smaller one — but the 32GB card is a nice sweet spot. It's a lot of storage, but you're not paying for an excessive amount that will just get wasted. And if you find you use your Raspberry Pi for more than the basics, this should be enough space to accommodate you.
Before buying a card, just think about how you'll use your Raspberry Pi. If it's only going to be used for something simple, a smaller card will be perfect. If you intend to install a bunch of games or use it as a home movie server, more storage will always be better.