Copperheads are excellent snakes to start with, although many suggest a rear-fanged species for a first venomous. I think the Copperhead is the best simply because of the lowered probability of a really dangerous envenomation.
In my experience, Copperheads are less agressive than rattlers, and of course much less agressive than their cousin the Cottonmouth. The potency of Copperhead venom is lower than other species as well. A reference chart comparing potency levels of snakes indigenous to the Southeast US is available at:
http://www.snakesofarkansas.com/index.php?jump=snake_bite.php