Does it make that much of a difference? Course the 2nd solution would be alot cheaper since multiple domains wouldn't ahve to be registered but does anyone know how well they work?
I would say it depends on what you are going to market. If you just plan on selling or pushing one product, then probably just have landingpage.com. But if it is going to be a site that you can build on and push a few products, then go with site.com/landingpage, then you can have site.com/landingpage1, 2, 3, etc.