With only 350k, your choice should be the Eagle. I don't recommend you buying the Viper unless you have at least 1 mil. A fully upgraded Viper will set you back around 2 to 2.5 mil, while you can comfortably equip an Eagle for 1/5 of that amount. The style of fighting is also different. If you have a Viper, use its speed advantage to boost to a distance, then make an attack run. In an Eagle, use its turn rate to stay on people's tails. However, both are pure combat vessels. If you want a little more utility, then go for the Adder at your budget.