That depends on your mindset and interest buddy, but anyway with my experience in blogging i will explain some basics of niche and web development in brief to help you decide the right niche to your blog.
If we speak ironically, if we say a blog a human body then the niche is like its soul, the success of your blog primarily depends on your niche, so choosing the right niche of a blog is the most crucial part of developing a blog.
If you want to be a successful blogger then your first step is to decide the perfect niche of your blog. Take your time and think properly and conduct some surveys before choosing your content.
As of your question, with my experience i would suggest you to go for a single niche blog since its has many advantages over multi niche blogs.
If the purpose of your blog is making money then single niche blog will serve you the best as it is easy to find direct advertisers. Its is difficult to manage a multi niche blog and it requires more time and people, it is practically not possible for a single person to develop and manage a multi niche blog or at least it is difficult since on must keep track of all the contents of the site.
The greatest disadvantage of multi niche site is that is has a negative impact on your site's SEO, in the present situation where millions of blogs come online everyday, SEO is one of the most important contributing factor of your blog's success. But in case of single niche website it is easy to do SEO on a single niche blog.
Another word of suggestion here is that, the chances of you becoming a successful blogger are higher when you develop a blog based on one subject that you are really interested and have better knowledge in subject.
So this my advice, Rest is for you to decide.
GOOD LUCK Buddy