You have to balance freedom of choice against deadlines and earnings potential. On HubPages you can write about what you know, what you are passionate about, and write the hub in your own time. For some writers this is paramount. Being free to choose the topic is all important too, because then you can concentrate on a niche area and build up a following or a core nucleus of hubs.
Freelancing can be a very stressful occupation. You not only have a deadline to meet, you have a word count and probably a keyword target which can be irritating.
Writing about something you're not interested in personally takes it out of you in time and the standards can start to drop. You see this all over the internet - budget articles pumped out at speed which often means bad grammar, weak sentence structure and an unreadable text.
To be a successful freelancer means having a thick skin and hardened attitude. Some manage it but they have to work long hours churning out stuff on any topic- not a job I could sustain! Plus, the fees aren't that great if the work is online. Magazines and newspapers pay much more.
HubPages allows you freedom but you won't become wealthy overnight, or even make a decent monthly income for the first few months (unless you're very savvy).