Use the optometrist to get the right prescription, and they'll also usually give you sample sizes of the brand they recommend, sometimes you have to try a few different ones to get the one that works well for you.
Once you get the right brand though, don't order your contacts through the optometrist, or at least compare prices first. My wife's optometrist wanted to charge her a huge amount and also lied and said it was illegal to buy contacts from anywhere else.
http://www.clearlycontacts.ca
http://www.visiondirect.com/
Or as mentioned 1800contacts.
These places sell the exact same contacts, often at 1/5th the price the optometrist will sell them for. My wife's had great service, if they screw up and send the wrong one getting an exchange is easy. Save tons of $$.