I currently have the 3G 8GB and it runs pretty slow because I use a lot of the memory. I want to upgrade to the iPhone 4 but don't know if I should go to the 16GB or jump up to the 32GB. Will the new phone take up more of the memory on its own that the 16GB might not be enough?
If you can afford to, just get the 32GB version. With the advent of HD video recording and a 5MP camera, you might find yourself running out of memory quite quickly. With the new Retina display, apps may also require more memory due to higher resolution graphics. Hope this makes sense!