If you're a photographer, videographer, content creator, or anything in between, then I highly recommend you splurge on the S24 Ultra if you can afford to do so. This model is the best out of the three for image quality and Samsung announced during it's unpacked event that it had partnered with Instagram to make S24 devices the first HDR-enabled smartphones for sharing photos on Instagram.
All of the models above are equipped with this feature, but only the S24 Ultra has the 200MP camera quality upgrade to ensure that you capture the best quality images. If you want more detail on this, I've written about why I think the S24 Ultra is THE phone for Instagram.
If the S24 Ultra is out of your budget, then the choice between the S24 and S24 Plus models can be tricky. The key differences to note are that the S24+ has the bigger display, improved battery life and slightly more RAM, so it might be the better choice for those who like to browse content and spend a lot of time on social media. If this isn't you, then you should be just fine with the standard S24 model if you can do without the larger 6.7-inch display.