I have a balance of both – i.e. the bonsai and the weed.
Why bonsai? Because some of my blogs grow at such a slow pace, they are almost not growing at all. By growing, I mean the pagerank, traffic and RSS subscriber numbers. Yet, I call it a bonsai because though they grow very slowly, the ad incomes from these blog are lucrative. One of my barely three months old blog has made a lot of money.
Meanwhile, I have my personal blog which grows and grows and yet, I don’t earn much from it. Recently, I notice an increase in traffic because of Google indexing. I saw an increase in organic traffic. Unfortunately, the income is almost stagnant.
So, between a fast growing blog and one that stays unknown, I will prefer building a few more of such bonsai blogs. My advice is not to be too fast or too impatient in seeing your blog growth. Fill it with lots of useful keywords and just sit back and wait for it to ‘mature’. Good luck in making money blogging.