Never send unsolicited email. That`s a potentially good way to irritate/alienate. Call them first!
I have to agree with Nikole. Of all of the cold calls I have made, I always, always ask their permission to send them an email. This way they know it is coming and even if they say yes with the intentions of deleting, you may catch their eye and on the other hand, they think your polite and trying to not be irritating.
The best practise will always be what you are best at. If you have great people skills, go with a cold call without email. If you can`t talk to people, simply call and ask their permission to send them an email.