This is one of the largest arguments among the web community. You have seen some become huge such as Darren R., John C, and many others which give the impression that you should throw everything you have into one main presence. Well I am able to make money online and make quite a bit by having multiple presences all targeted towards different topics and niches. Personally I get bored about writing on the same topic day in and day out so I decided to rely on the multiple website approach rather than throwing everything I had into one presence. This actually works out great for me as long as I create mainly static websites. I can update them once every month or so and keep my rank (as long as I build backlinks steadily as well). So I guess this is more of a question what will work better for you rather than what works because they both work great.
A few reasons one main presence may be the best for you is the amount of time. The reason I build many websites is I have 24 hours per day I can work online so I have the time to create and market all I want. If you have a job which you are not allowed to work online then this will of course be much more limited. For you I would recommend only running one website and spend all the time you can creating content and marketing the presence. You will find yourself running low on Free Web Traffic if you try and spread your internet marketing across many different platforms if you only have a limited amount of time you can market. To reach and hold the top for a few keywords is actually quite a bit of work and can only be done by a handful of people. So for the best chance go for one main presence and keep everything there.
If you have plenty of time to work and are have a hard time focusing on one topic for an extended amount of time then multiple website creation will be best. This will also be the best option if you can not afford hosting. The reason for this is if you use free resources such as myself and throw everything into it then expect to pass the limits and run into a bunch of downtime. On the other hand if you spread your websites out then you are much less likely to pass the limits and shut your income streams down. Another reason I personally like running many different presences is I get to market them off each other. This means free backlinks from high authority websites and pages. This is a great way to jump start an internet marketing campaign for a new page or website so take it into consideration when trying to figure out which would work best for you.
Whether you choose the first or second way monetization should be a consideration and these paid survey affiliate programs are great.