Let's see... I know this is basically closed and all but just wanted to give my opinion.
Arbok has Intimidate and Shed Skin, while Seviper only has Shed Skin. This gives Arbok an advantage over Seviper. Seviper has better Offensive stats while Arbok has more defensive stats, so I guess Seviper has it on that category... even thou Arbok is slightly faster. True on Seviper having a better Offensive move pool while Arbok has better Defensive move pool. They both get Coil move which is awesome which raises they Attack, Defensive and Accuracy meaning Gunk Shot becomes more deadly and this on a Arbok can become a problem, oh not mentioning that ARbok gets access to the Elemental Fangs while Seviper doesn't... I would just say Arbok, you can have a better strategy with it. If we going by looks than Seviper ^^