I don't have that much PvP experience... but I have fought some people. Here's my experience:
The Vulture is not fast, but agile. It has good survivability for its size and the two C3 hardpoints provide plenty of firepower.
The Vulture can deal with small as well as large ships, thanks to its great combination of agility and firepower.
This all works really well... until the day the enemy you're shooting at isn't a Sidewinder in Eravate or a Type 7 in Lave that probably only is going to combat log anyway. The firepower of the Vulture is great, but of no use if your guns are pointing away from the enemy. The manueverability is also great but of no use when you're desperately flying in a straight line trying to get as far away as possible from the horde of Eagle and Cobra-peasants that were as contemptible as to cooperate against you, and they might not even be fully A-graded! The horror!
As someone who have fought as a leader of said peasant-squad, I have many fond memories of firing upon and ramming multiple times into the engine exhaust of my panicking Vulture-enemies.
Now, Vipers on the other hand, they tend to be a lot more slippery. High boost speed, some corkscrew manuevers, maybe a little chaff and ECM ready just in case... they're pretty good at running away.
I've seen people load the medium hardpoints with lasers and the two small with torpedo tubes. Torpedoes can do a lot of damage, and if you fire them while close to and approaching the target, there's a good chance that Pd will not be capable of dealing with the torpedoes.
If you want to go into PvP-heavy warzones, I think there is reason to choose the Viper over the Vulture. You're not invulnerable, of course, but the Viper does have the additional advantage of costing much less to rebuy, as well as being generally underestimated compared to the Vulture.
For myself, I use the Cobra, but this is partially because I do a lot of non-combat stuff.
