This one, (recflying) is very good, and if yours becomes this good it'd be very hard to move it from a poor (read cheap, or free) platform, to another one if you wanted to, especially without effectively starting again.
So you need to have a good understanding of what your site might end up as, and how expandable/developable the software is/will be.
Not to take anything away from Recflying, but the very best platform that I know of, with the best features, support, development etc is the one HBA uses - there's a link in my signature and developer details at the bottom of each page, but it's far from free software... expect around $10k for a basic template. Then, as Ian alluded to, expect to pay a full-time IT man to deal with spam and other idiots. The bigger the site becomes, the bigger the attacks it will attract.
Quality blog sites carry heavy ongoing costs and workload, so it requires a big commitment or will assuredly join the smoking heap of previous well-intentioned projects.