To be honest, if you can afford to render to 1080p, always do. Quality between 720p and 1080p IS noticeable and you will be able to stand out from the crowd by uploading high video quality. For instance I am one of the very very few on Youtube who has a Half-Life 2 playthrough in crisp 1080p.
A few solutions to help overcome the hurdles of 1080p:
1. Computer hardware. A fast (preferably overclocked) CPU and a powerful GPU can drastically reduce rendering time. With my hardware I render a 15 minute 1080p video in about half an hour.
2. Internet connection. The biggest reason people don't render to 1080p is because it doubles your file size and thus your upload time. If you can, try investing in a fiber connection where download and upload speeds are the same. Not every country is fortunate enough to have those connections yet, but if you do I highly suggest getting one. I have a 100mb upload connection which obviously makes uploading large files a breeze. Usually takes me less than 10 minutes to upload a 2GB file.
Good luck!