I am designing a site SEO point of views? please help me

I want to ask that should i use the banners in my site , I am not favor of adding the banners in the website because of reduce the time of website downloading. another way to optimize the image in ALT attribute , i can add the images also to optimize the images.Now my question is Should i use the banners or images so that i optimize the image with ALT attribute.or If a give the ALT attribute in the logo of the website then it would be harm for me because it is common for all landing pages.