Need to rebuild my banners what is best now
 

I got a lot of banners but they are getting pretty gold and most of them are in GIF format.
Google Page Speed really seems to hate them saying to replace them with mp4 ads instead.

I tried converting them from Gif to MP4 and that worked kind of, it helped the speed increase
but been having problems on one of my hosts for them even showing up in Firefox for some reason, yes the exact same code is on another host and works fine, could be a cache issue

What is the go to ad format these days? html5 ads, mp4 ads? I need to get back in the game on them,

thoughts and might be looking for a new designer as well.