Unless you're talking about your own personal sites, a better question might be 'What's the right font for my client?'

Tim Brown from Typekit has some excellent thoughts on this:

http://vimeo.com/17079380

I'm Chinese, so the situation is more complicated.

For iOS app English version, Helvetica Neue. For Android app English version, Roboto. For iOS app Simplified Chinese version, Heiti SC. For Android app Simplified Chinese version, Source Han Sans, or Google called Noto Sans CJK, these two are a same typeface.

And for web, I prefer Avenir Next.

Unlike Latin fonts have tens of thousand kinds, Simplified Chinese font is probably less than 500. And the good font is very expensive. Because a Chinese font contain at least 6763 characters. Well, that's only one weight. So design a Chinese typeface cost lots of money and time.

Take a look at this post I made about a year ago. There are some really good recommendations in here.

https://news.layervault.com/stories/10125

I'd love to see this thread get an update though! There are a lot of great fonts out there that I'm sure haven't been mentioned yet.

Roboto since one year.

It depends on the project and client. When I'm doing a side project I mostly use one of these:

Proxima Nova, Gotham, Whitney, Didot, Avenir.

Source Sans Pro and Source Serif Pro are my favorite at the moment.

Freight Text and Freight Display are wonderful for body text at larger (16-20px) sizes.

It depends on the context.

I really love Proxima Nova, Open Sans and Montserrat.

Proxima Nova, in all of it's weights and performance at smaller sizes is a solid contender, however, I'm always put off by it's over use.

The key is finding something that gives you typographic flexibility but also adds to the overall brand of the site/product/service you're designing to help establish a point of difference from other sites/products/services.

I'm going through a "Source Sans Pro" stage right now. This usually changes when a new font comes out. In the past I was an Open Sans and Lato fanboy.

If you're looking for font inspiration you should check out http://FontGala.com

Avenir Next has been my go to lately.

I prefer Proxima Nova, Open Sans, Lato for English and Hiragino Sans GB for Chinese.

As much as I love (loooove) Open Sans, I don't like using it for app UI design because the kerning can often get crazy.

On the web, you can manually fix it. There are lots of CSS/JS/combo solutions.

In apps, it's just a hassle. Plus, it's often a good practice to start with whatever the system default is (to that everything fits in), but that's probably a personal preference.

To me, legibility is the most important aspect to consider for body text, so I usually lean towards using something with proven legibility such as Georgia, or a sans serif like Helvetica or Lato.

For Graphics, titles or shorter lines of text, I would usually pick a font that works for the style/mood/brand etc. This would be where I would look for uniqueness or personality. I have worked on many different types of projects in many different industries so it is often determined in during the style exploration process and is very much project by project.

Pretty big fan of Noto Sans these days.

Din Next LT Pro!

My most used interface fonts this year were

DIN OT, Open Sans, and Helvetica Neue.

Roboto (2014) has become my go-to font for all UI works, but before that I frequently used Lato, Open Sans and PT Sans, which is excellent.

If you never used PT Sans, go give it a try!

Source Sans and Open Sans are really a godsgift for this I think. Helvetica Neue keeps working too and Roboto too ofcourse

I'm going through a Raleway phase nowadays, trying not to overuse Proxima Nova! There's great potential for Raleway, being available in both Google Fonts and Typekit

Freight Sans Pro also usually gets some love from me.

Avenir, Helvetica Neue and Open Sans.

I use Proxima Nova, Lato and Open Sans :)

It depends on project but generally I prefer Open Sans and Myriad Pro.

Open Sans works great – it's clean, readable and multiingual