How about choosing one that your team knows better? Your startup's app is not a good place to learn new technology, as proven by Reddit and Twitter, among others.
Yea, Reddit and Twitter are great examples of places that failed because they were afraid to learn new technology? Wait. That failed because they tried to learn and implement things in unfamiliar technologies? Oh, wait, what?
No, they tried to build the app with a technology they wanted to learn {Reddit : Lisp, Twitter: Rails} and then had to rewrite it (mostly) from scratch when that didn't work out {Reddit: Python, Twitter: Scala}.
Neither failed, because they were smart enough to know when to ditch. God knows how many startups failed because they didn't know that.
For Twitter, Rails was the technology they knew. They decided it wasn't the right tool for their needs. Scala is the tech they learned (and continue to learn) on the job. They even have a group blog detailing this process (http://gracelessfailures.com).
