On after effects I have been having a problem with rendering as when i try to render a video with a regular 3.2 PAR (Pixel aspect ratio) after effects resizes it from MP4's 1920x1080 to 720x1080 and this is really bad for the video quality, i have tried changing the PAR to 5.1 and this does stop the resizing but it makes my video quality terrible, Please help me if you can.
I think you might be confusing pixel aspect ratios with image aspect ratios.
I suspect you want square pixels - ie a pixel aspect ratio (PAR) of 1:1
Most HD videos are 1920x1080, which is an image aspect radio of 1.778 to 1. Most HD videos have a pixel aspect ratio of 1:1.
Is your desired image size actually 1280x720 ? I suspect it is, rather than 720x1280 (720 horizontal x 1280 vertical).
Non-square pixels are only usually used for SD widescreen videos - more of a legacy requirement these days. Unless maybe you're designing for a specific custom display like a big advertising screen or something like that?