Really depends on how much fun you want to have. My personal favorite is Ptyas carinatus. Four meters of 'fun'. We had a blast but they are huge and vicious. They mimic the king cobra (look at the pattern on the snake in the pics, sure looks awfully king like) and bite just as hard, just lacking big glands and hypodermic teeth.
However, they can really hit you hard. Watch the 'Snake Savior' of Nat Geo's 'Snake Wranglers'. Some assistant reptile chick in India tries to tail one. Pays for it with an absolutely brutal chomp to the face. The snake then pissed off, using her arms as a launching pad. We of course rewatched it many times. We finally worked it out. Just before she gets nailed, a split second, some guy says something to her, she flicker her head slightly, light reflects of glasses. Snakes smacks her a good one. Too funny. The best part was that the cameraman had just panned off of the snake and was doing a close up on her face. Bang. Right in frame. A true professional.
For a lest brutal species, try Coelognathus radiatus, the radiated rat snake. We had about fifty at a fime a few times in our research collection. About two meters in length and utterly psychotic. But with a snake hook and tailing them, its no worries. We actually used them as starter snakes to get people up to speed with venomous 
Some of the more aggresive ones are also some of the most beautiful. Spilotes for one are stunning snakes from Central America. Not a real drama to work with. Gonyosoma are actually quite nasty but since they are so much stronger (and more arboreal) they can be much more of a pain than the C. radiatus.
Some of the other Ptyas can be easier to work with and ironically some of the smaller ones are also some of the most beautiful. There are some green ones coming out of Hong Kong that are very sharp and only about two meters.
As a taxonomical aside, Coelognathus radiatus used to be in Elaphe along with a pretty impressive collection of other snakes that only superficially resembled each other. Just as anything that wasn't conveniently an elapid or viper, became a colubrid. Thats all been sorted out now. One of the most conpicous findings has been that C. radiatus is not even a ratsnake at all but are actually closer to a racer (Coluber has been another dumping ground but still remains to be sorted out fully). Its certainly deep with in the Colubinae family (Colubridae as a family is toast, there are several deeply split ancient lineages there. )
There are just so many others to choose from, its really a matter of chosing your poison. But be careful. Virtually all the 'colubrids' still have the ancestral venom gland. Some of these, such as Psammophis for example, are quite dangerous and may be able to cause lethal bites. This has happened before, Rhabdophis was just considered a genus of cool Asian 'gartersnakes' and were hugely popular in the early 80s pet trades till they killed a few people in Asia and hamered some kids who bought them in pet stores. There is also the boomslang and twig snakes and two dead eminent herpetologists not too long after each other. So, as you wander through the merry world of the advanced snakes, keep that in mind.
Cheers
BGF
Ptyas carinatus pics