When making contact with a new prospect, which is best: phone or email?

If it's your "ideal customer" you're going after, then I would suggest prime them a little before hand. Email first, see if they are active on social media, blogs, linkedin blogs etc, start to comment on their activity. So eventually when you do call them there is a more recognition rather than fully cold. 

Your first email most likely won't be read, but if it is read I would suggest you tell them you are going to call at a certain time. It takes the surprise element away from the call. 

​If you really wanna be a pro... do your research on that person. Scour their LinkedIn, blogs, facebook, find out what they are interested in. Use that thing to create a personable connection. (be careful not to be a creepster here whatever you eventually do say, make sure you don't sound like a stalker. When emailing, don't talk business in your first line. Be interesting, thoughtful, and relatable.