I currently keep a 9-foot adult male Yellow Anaconda (Eunectes notaeus) which I got from a young guy who couldn't deal with it anymore when it was less than three feet long!
Even a relatively small Yellow can be a heck of a handful - 'condas are one of, if not THE most powerful snakes there are... I wouldn't want to deal with a big Green 'conda.
I generally do not handle my animal, as I have been "nipped" by him twice - he's basically a specimen to just look at and admire...he comes out for cage cleaning and then basically goes right back in.
I've been keeping snakes for years, and I'd never even consider keeping a Green Anaconda (E. murinus) - it's just too much for the average keeper to deal with, in my humble opinion.
Something people don't realize is the fact that a big constrictor can kill you MUCH faster than even the most venomous snake - how long can you hold your breath - two minutes, maybe..?
I've been grabbed by a largish Burmese Python in full-on "feeding mode" and believe me, it's something that you do NOT want to experience.
So, if I were you, I'd definitely go with something along the lines of a Carpet Python, Ball Python, Common Boa Constrictor, etc...
If you're worried about being nipped, remember, if you keep snakes you WILL get bitten every now and then...and it's usually the fault of the keeper...
Cheers, and good luck withhn whatever you decide on!
Simon