There are a zillion blogs out there, and it may seem like your own, little independent blog will just get lost.
So, the allure of writing for another site, perhaps for someone else perhaps more established than you, may seem to be the best way to go.
It isn't. Unless they are paying you well for your work, don't, I repeat don't, write for someone else's site/blog. If you want to maintain your own voice, and have full control over your own content, create your own.
The worst thing any blogger can do is to go write for another site, for no/minimal pay, and with no clear agreement over who controls the blog.
What is a blog anyway? Some people take it to mean underlying software that runs it - Wordpress, Movable Type, LiveJournal, Blogger, what have you. Some people think it's the format of posting dated articles in a regular basis.
I think the fundamental purpose of a blog is to allow the writer to publish his/her own words, and have ownership of those words. In that context, writing for other people does not make any sense at all.
Ask yourself: what is the purpose for you to have a blog?
The exception is if you're getting paid for it, but be sure that your words are not being undervalued either. And be sure that you have a clearly written out contract before you start over who owns your words, and who has the right to edit those words. When you take a paying blogging gig, it is just the same as any paid writing gig. Professional writers make sure to know how far ownership of their writing extends to either party. You should too. Do not let people undervalue you because you're 'just a blogger'. People who come from so-called traditional media especially tend to do this. Maybe they're scared of the competition, or maybe they are just unaware.
If you have confidence in your subject and your writing, if you have random strangers reading your blog and even sticking with you as an audience, take confidence in the fact that you are a good writer. And make sure that others know this too. Do not undervalue yourself.
Merry Christmas!