CBZ is the format most often supported by comic readers (basically a plain ZIP file full of images). I believe there are Android comic readers that can do automatic panel detection but given these are purely software-based they can sometimes miss panels, mess up the panel sequence, etc. for pages with complex layouts.
Guided View is proprietary and initially came from comiXology (which Amazon acquired in 2014). At least back in its early days, there was an actual human reviewing the panels iirc so it was a mix of software-based panel detection and manpower for fine-tuning. In the US, one can buy comics from Amazon and get both Kindle and comiXology versions (but not the reverse). I'm not sure if it's the same situation in UK.
Personally, I buy on Amazon so I can easily liberate my comics and have DRM-free copies for posterity. However, I tend to prefer using the comiXology app over Kindle for automatic series grouping and really, better overall metadata and organization.
comiXology tends to have higher quality, too. For example, Black Monday Murders Vol. 1 (Hickman, Coker):
- comiXology: 250MB
- azw3 download: 47.5MB
- Amazon website: 179,584KB (only accessible via Kindle for PC/Mac 1.19+ and Android/iOS apps, and includes duplicate HQ and LQ images anyway)