Android was definitely faster to respond, but in order to send the message you have to press Send. Siri took her time, but you can send it without having to look at your phone again. So speed goes to Android, but if you're clumsy or slow-fingered, call it a push.
Navigation: Google Voice Actions
No surprise here. Android has integrated turn-by-turn navigation and the iPhone only gives you directions. Kind of an unfair test in terms of final result, but even discounting that, Android's map was up first. (Note: this was an indoor test, so neither could get a GPS lock).
Memo: Google Voice Actions
This was a close one because there is some personal preference involved; both devices managed to screw something up. Android was definitely faster, but the two platforms handle notes differently. With Voice Actions, in order to save the note you have to hit Send. The reason is that it's actually just emailing the note to your personal email address (though you can add recipients, BCC, etc.) which takes a bit more time.
The iPhone saves your memo directly into your Notes app without you having to hit anything else. While that's an advantage in convenience, on Android you'll have access to your note anywhere you have access to your email address. You can sync Notes with your Apple account, but most people haven't and email is way more convenient. Plus, Voice Search actually sends the audio recording of the voice note as an attachment in the email, so if you're in a loud area and the transcription wasn't good, you can still hear it later. Advantage (for both speed and convenience): Android.
Calendar Management: Siri
Siri can add appointments to your calendar. Google Voice Actions can't. No contest.
Browser: Google Voice Actions
Voice Actions was clearly just much faster on this one. Plus, it went directly to Gizmodo.com where as the Siri went to Google's search results for Gizmodo.com.
In terms of speed Android was just a little bit faster, but the iPhone's results were better formatted. Plus, with Siri you can ask, "What will the weather be on Thursday in Brooklyn, NY" where as Voice Actions won't understand that.
Unit Conversion: Tie
This one was a dead-heat. Google's results came from, well, Google. Siri's came from Wolfram Alpha. Both were fast and both were right.
Overall Winner: Google Voice Actions
In terms of speed and accuracy, Google Voice Actions was ahead in almost all of our tests. Both have strengths and weaknesses, and both are handy convenience features. Siri has a little more colloquial chops and is more "fun," but Voice Search is ultimately a faster, more efficient tool. In terms of performance, the green robot takes the win. We'll test again when the next generation of these programs are out in the wild.
Siri may be able to do a few extra things, but it's cool to see Google Voice Actions is mostly faster and in some cases better than Siri at the things both can do.