Looking to buy a micro ad card for my new hero4 session. It can take up to 128gb I think so I may as well got for the biggest I can.
What type do I need or what type is best for bike footage. I know nothing about these things

Avoid anything vaguely cheap, the cheap ones seem to result in crashes and only seem to allow the camera to record 3 or 4 seconds of footage.

Make sure it’s class 10. Cheap is OK, but I would definitely buy from a reputable seller and avoid eBay – there are loads of fake cards out there which will at best limit your recording time (they don’t write fast enough to ‘keep up’) and at worst lose footage because the card isn’t as capacious as it claims to be and overwrites itself.

Ive seen some sandisk and Samsung cards. I take it there as good as one another?

GoPro recommend certain cards here –

https://gopro.com/help/articles/Block/microSD-Card-Considerations

I use one of these without issues –

https://www.amazon.co.uk/gp/product/B013P1M436/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I went through the same recently as got one for holiday.
SanDisk seem to have a better read/write speed for the same amount of money, make sure that you get class 10 and as above definitely get from a reputable seller. I have found that Currys are the same price as the online retailers for once for the SanDisk Extreme Plus 64gb @ £29.99

I’ve had at least 2 sandisk cards fail, so I tend to avoid them now. I get mine from mymemory.co.uk the own brand ones are cheap, good enough and have been reliable so far (touches, head, desk and lap)

touches, head, desk and lap

you have wooden legs?? or just wood between your legs?? 😯