Picking the right microSD is easy. It completely depends on your device and I do not recommend buying anything more fancy than neccessary, as nobody knows what the next generation will need.
If your main goal is to shoot video (e.g. with a Osmo Pocket III) you want to look out for specific ratings. The relevant ones being the UHS-Bus displayed in roman numerals I or II. Check your camera manuael if it does support UHS-II. If not, just buy UHS-I as it is cheaper. Then there is the VSC-rating of V30, V60 or V90. V30 gives you at least 4k 30FPS. If your camera can do more VS60 might be worth it. Again check your cameras manual. Lastly there is the old U-rating U1 and U3. You want to make sure the card has U3.
Buying a microSD for taking photos is the easiest. You just want to check your camera manuael if it supports UHS-I or UHS-II and choose it accordingly. Stick to a known brand like Transcend, SanDisk or Lexar.
If you want to use memory card for some form ouf mini computer you mostly want to look out for the A-rating. This one spicifies how many file interactions are possible per second. That is different from speed which might just define how fast or slow one file might be written. There is only A1 and A2. Just make sure the card has A2 printed on it. If it also has V30 or U3 printed on it you can expect 30Mb/s which is a good mark. If you just play around off brand cards might be a way to safe money, but I generally recommend to stick to known brands like SanDisk or Transcend.