superior, for dense information? Helvetica. Perhaps, if you like Frutiger's work better, you could try to go on with Univers (I guess they have an Univers Next version for digital media), but Helvetica is the font for text on screen, period. That's why it's used for such applications, and that's why it's the default font on Windows (Arial is close to Helvetica), OS X, and pre-ubuntu linuxes (ubuntu uses a Dalton Maag font called - surprise - Ubuntu, that supports all major languages).
Personally, I don't think there's a superior font for Helvetica.
But readability is not just a choice based on the font itself: you need to take into account the actual font rendering system used (text on OS X is much more readable than on Windows because of the different anti-aliasing technology), of course the font size, but also line-spacing, word-spacing and letter-spacing. You can bring out different effects from the plain old Helvetica just by increasing its line-spacing and combining it with other sans-serifs.
Every single foundry who has created a webfont claims they've designed their font for readability, but gosh!
Most US-designed fonts on Google webfonts don't even support Latin-1, and when it comes to Latin-2, or asian character sets, they're dropped dead. This applies to PT Sans, the body font for Smashing Magazine, it doesn't support Latin-2.
You can get away with two or three fonts for the application so it won't be that monotonic.
Verdana was designed for screens in the 90s, but it was done so with much lower resolution (as in, points-per inch) screens than what we have today. I don't think we need Verdana today, although I wouldn't say you shouldn't use it.
You can try out font combinations with Google Fonts on font-combinator and you can download its sourcecode in case you need any modifications to it.
Smashing Magazine has an excellent collection of articles on how to choose fonts, like here or here.
You can read about typography in Bringhurst's The Element of Typographic Style (applied to digital media here) which is considered the modern typographic Bible, or Tischold's The New Typography, which is a nearly hundred-years-old title.
So, no, I agree with those in the film Helvetica that there's no superior font than Helvetica.
But perhaps it's just my style...
(And truth to be told, I also use Avenir Next (the optimized-for-digital version) in one of my main projects just for that subtle mood-changing effect it has... Helvetica is neutral, Avenir is a bit, a tiny bit different)
