Hello,
i'd like to know what better to use in developing for iOS devices?

i know that pngs a better quality format, but jpg's weights less and i dont know how ios handles jpgs if handles at all

Depends on...

If you need transparency/alpha channel you need PNG.
If you have just a lot of photos without the need of special shapes or transparency most cases JPEG can compress better with acceptable quality.
Computer created images with simple structure (no complex textures) and high contrast lines most case PNG can compress very good and you would see JPEG artifacts and a loss in color brilliance with JPEG compression.

So it's a case for try out or experience...

Both work on iOS devices. PNG has lossless compression and works best with images without gradients (logos, vector graphics). On the other hand high quality JPEG is a better choise for photos and other complex graphics with gradients (much smaller file size). If you are not sure, you can always compare the file sizes.

thanks for answers