First person 100%.

But try to avoid "I" as much as possible. The more you can generalise and universalise your experience, the more it brings readers in and the more powerful it becomes. For example:

"I've never liked standing in a bank queue"

becomes:

"No one likes standing in a bank queue"

Instantly your column is about all of us/your readers, rather than just you. Obviously if it's a divided issue, you can't speak for all readers. So you might begin with: "Many of us struggle to parallel park" rather than "Everyone struggles to parallel park" (which will insult and alienate those that manage it just fine).

Do feel free to include personal anecdotes and stories, people love them, just cut out as many uses of "I" and "me" as you can.

If you are a pivotal part of the brand (you, yourself, your image, etc.) than I would write in the 1st person because it seems more authentic and approachable. You want to connect with your audience and customers as if in a conversation.

I feel that 3rd person should be reserved for more formal items (press release, loan proposal, etc.)

Always in the 1st person when it is a personal site and profile. Jef is correct.