Popular ones!  That is the simplest answer!  Traffic converts to making money blogging.
Besides being popular and having lots of traffic, WHAT you blog about is important, and some topics do better than others.  But it is not the topic that drives it, it is the audience.  So to determine what kind of blogs make money, you have to know what audience converts to advertising sales!  And the top answer for that is…Moms.

Any blog whose primary audience is Moms will have the most potential to make money with advertising.  So, some of those types of blogs are:

Home Decor, Food, Lifestyle, Kids, Beauty, Health

These are also the blog categories most saturated with blogs.  So it is more difficult to stand out.  You could have a blog in one of the most beloved Mom-niches, but if you don’t get traffic, you won’t make money.
In my blog post “How much Money can I make Blogging”, I say that if you can get your traffic to 2,000 pageviews per month, then you should expect to make around $10 per month in advertising with Adsense.  But if you have an E-book or some kind of helpful printables to sell, you could make $10 per month way before you even reach the 2,000pvs.

There are many other ways to make money from a blog besides advertising, but I think that the “passive income” from advertising is what most of you are most curious about in answering this question!
What I want you to get from this post is that if you have a passion to blog about something, you can make money.  I started blogging in photography because I am passionate about it.  I am a Mom and I love being a mom and have a ton of creative mom ideas.  But the mom-blog  place just doesn’t fit me.  You have to know what you love and blog about it with passion.  THAT is what will bring in readers, and eventually you WILL make money at it.  ALL KINDS of blogs CAN make money.  But passionate bloggers make the easiest money, quicker!