The question whether to build a niche blog or general blog daunts many. Answer can only be given by considering various factors like monetization, time invested, looking for ROI (Return on Investment) etc. Understanding these factors will provide clear answer regarding whether to choose a niche or general blog.
Investment of Time & Money:
The first factor to consider is whether you have sufficient time to invest. Generally, a single person handles the content. Therefore, it is obvious that sufficient time should be spared. However, you can also hire a writer. Hiring a writer, on the other hand, requires investment of money. Ask yourself whether you have sufficient time and money.
In case, you lack both, then a general blog/site is perfect. General blogs have numerous categories. These numerous categories give flexibility to write on vast areas. Furthermore, content can be funneled through guest bloggers. Depending completely on guest bloggers is not wise, though they provide constant stream of content. Moreover, there is always a need to customize design. Unless a developer, you might want to think about outsourcing web development.
Many wish to earn as affiliates while other through Ads (preferably AdSense). Monetization technique decides whether to choose a niche or general blog. Affiliate sale does better only in niche sites as obviously readers are looking for products related to the niche.
AdSense ad does better with general blog. The Click through Rate of AdSense ads is higher in general sites. Readers of niche site know what they are searching. Therefore, they hardly click on ads (unless it is related to the niche). If you are looking to earn through AdSense then general blog/site will prove beneficial.
Reader Ship and Engagement:
This one is obvious. General blogs have less or no engagement while niche sites engage highly. Readership and engagement may not be of concern to many. However, for those who are looking to advertise their service or product should take care of engagement.
In case you have decided a general blog then you have to understand, that most advertising network do not approve your application (eg: buysellads.com). With Adsense you are safe but if banned then finding another equivalent network is difficult. Therefore, balance your engagement of your readers to be safe.
Personally, I have noticed that general category blogs/sites get high rankings with ease. For instance, they gain 50k Alexa rank within a short time. Later they move a further to 30k (rarely do they touch 15k mark) then again move down to 70k and 90k. Later, again they start their climb until 30k and back to lower rankings. The reason for back and forth motion with ranking is that the site/blog is saturated. No new readers are gained after a period. Moreover, old readers move on the other sites. To conclude there is no loyalty of readers for continuous growth.
With niche sites, constant growth is evident though there may not be instant traffic gain. Readers are loyal and frequently visit the site. In short, readers keep on accruing and therefore there is no major rank retrace. Alexa rank of 1k or less is possible provided the niche is in high demand.
Return on Investment:
With respect to ROI, niche sites are more profitable. Interestingly general sites do not require for much investment. The investment on a single niche site can be compared to four or five general sites. Now, if we look at the ROI between a single niche site and five general blogs then ROI can be said as equal.
Finally, with these factors it is your decision whether to choose a niche or general site.