Codec question

What is the most widely used codec for video and audio that will provide the most compatibility across devices such as iphone/ipad/android/plex/kodi ? without having to transcode much on the server/client ends in general ?

is it H264/aac or some other combination?

I am slowly transitioning my kodi setup to plex and before it wasn’t a problem of having any codec’s since the transcode happens on kodi devices but on plex the transcoding happens on the server and with multiple streams it gets a bit overloaded.

Video: H264, level 4.1, optimized for streaming in an mp4 container.
Audio: AAC or AC3
Subs: SRT
I avoid subtitles if at all possible, otherwise I hard encode them(burn) them into the video.