Seriously, why don't you just learn HTML/CSS/php/JS/CS instead? No offence, but the fact that many "Website Builders" exist is just bad.
When you build a website, you need to care about SEO. Site speed affects SEO, this is one of many reasons why you shouldn't use a website builder. If you want to make a blog, go ahread and use WordPress. If you want to make a wiki page, use MediaWiki, but if you want to create a website, use Notepad and do some coding!
Once you get used with margins, paddings and borders, website creation is easy using HTML/CSS, styling wise. Rest is some php to do queries and fix security and JavaScript of CoffeeScript to make effects and checks. In my opinion, it is more easier to use all those programming languages I mentioned than GS2.