I am into iOS development from past 1+ months and what I have experienced is that I have to put images for 1x 2x 3x for iphone and then 2x retina for ipad. One of the experienced designers has sugguested to me to go for svg format as it scales itself according to the screen sizes.
So my elaborated questions are:
If any other information according to your experience please share.
Thank you.
Official iOS Dev documentation says "the PNG format is the one most recommended for use in your apps". You can read it for a lot more information here.
You could use vectorized PDFs alternatively. You can read more here. It isn't without limitations, but with vectorized PDFs, Xcode automatically generates scaled versions. That should make life easier. Note that sometimes the scaled results look quite poor.