Looking at phone replacement S23 ultra or iPhone 15 pro

[lokijet]

Previously always been a Samsung girl but am feeling tempted to the dark side.....

I know they are both good phones - any views on pro/ cons

Can you use WhatsApp on iPhone ? (I can't on iPad)

I can't see a 1TB version of the Samsung but also wondering if I would ever need that much

There aren’t really any pros and cons I can think of at the moment – I think that it just depends on what you’re used to, and how tolerant to change you are. Like you said, they’re both good phones.
Yes, you can use WhatsApp on iPhone, but you need to make sure to transfer your message history over to the new phone correctly. (I’m sure that there are lots of helpful videos about this on YouTube)
As for storage, it really depends on how much have right now. If you’re feeling concious of how much you have remaining often, it’d be a good idea to increase it, but if you’re not having any issues, I’d just keep it at the same size as your current phone. I’d say that 1TB is unnecessary unless you do some sort of video-filming as a hobby/job, or work with large files on a day-to-day basis.