Small Niche Site or Big General Site?Which is better?

Many people said that niche site with keyword in the domain is super easy to rank high in Google and thus it can bring ideal
traffic in a rather short time.Someone even said that he just write one article for his small niche site and still rank high.

In my opinion,these big general sites like about.com can easily rank #1 with the keywords the small niche site relies on if they wish.So why don't we build a bigger site and then discover keywords in the same way as you do with small niche sites?That can rank even higher.And you don't have to buy so many hostings and domain names.

Tell me your idea.