For the sake of reaching simplicity in maintaining my web application code, I've decided to keep my login/register forms in a separate page and load them on demand via a modal popup window. This causes a little lag/delay when clicking on corresponding opener buttons but lead to avoiding mixing lots of code and many pages of my web application cause I've make these two buttons available in all my external (non logged-in) pages.
I've seen many websites that make their login/register forms a hidden part of pages so that clicking on opener buttons leads to instantly opening these forms containing frames.
What is the best practice for integrating these forms with parent pages? making them a part of every single page (even though no one click on them) and consequently increasing the volume of page or keeping them seperate and loading them via a container mechanism (e.g. like pop-ups)?