When you write an article, do you write ''ten years ago'' or ''10 years ago'' ?? Personnel, I use letters to write low numbers only (0 to 20). What about you ?
When I wrote for a newspaper, the guidelines (AP) were that anything under 10 is spelled out, but if you have a list of numbers that includes 10, be consistent and write them all as numbers. Here are some helpful links: http://www.dailywritingtips.com/10-rules-for-writing-numbers-and-numerals/ http://mtsu32.mtsu.edu:11178/171/tips.htm#numerals
When I'm doing pro writing, I use AP. It's what I learned in journalism school and I like it. I only deviate if it's required by the client. However, when I'm whipping up stuff for myself for Adsense, affiliate proggys, newsletters, etc, I use whatever the heck I want. Usually that AP still. It's branded on me.
Usually AP as well unless working on my own blog posts or something where that doesn't matter (then I go with whatever looks better / has more impact).
As what others have already mentioned, there's the journ school staple, spell it out for numbers below then, then use digits for numbers 10 up. Just remember to spell it out whatever the number is at the beginning of a sentence.
I spell it out. Depending on how it lines up, I'll sometimes spell out higher numbers than twenty. It depends. If a number is at the end of a sentence, I spell it out. If it needs to be pluralized, I spell it out. etc. etc.
It varies for me. Sometimes seeing a number is simply more effective and eye catching on a medium that most scan rather than read like the Internet. I start with AP and sometimes switch if a meaningful number gets lost among the words on the page.
i prefer number.. so there are more variations in your article, not just bunch of letter, at least that's my opinion