whatever species of rattlers used by the various offshoots of baptist churches that practice snake handling seem to be pretty darn relaxed about being handled. Yeah, they bite sometimes.

From my experiences with wild venomous snakes, I'd be more than willing to bet that there are venomous species that are calmer and less agressive and there are species that are more agressive, and it can't be judged by looks.

I've never met a nice water moccasin/cottonmouth. Any that I have come anywhere near to have shown aggression.

I have met many "nice" copperheads, or at least, they certainly didn't mind being picked up by a nice long stick and moved off the foot path.

I'm fairly convinced that cobras are relatively calm hots, but have no personal experience other than seeing them around other people and in zoos. The biggie, probably a 10+ footer king, that they had at the houston zoo back when I was 7 was pretty unconcerned when his daily cage cleaner walked around the cage with a spray bottle and wiped down the glass walls. And whenever cobras do get defensive, they have just about the slowest strike speed of any snake I've ever seen strike on TV or elsewhere.