Both are viable, playstyles are quite different though. Lightning will always be better in p8 games.
Nova is fun, faster on p3 or lower, tankier. Way less gear flexibility since you almost have to use 2h inf wep so you're locked on most gear slots to hit fcr bp. Less mf as well
Lightning has higher damage, less tanky but a 'safer' playstyle. Way more gear flexibility and easy to get a lot of mf. You can run 3 piece tals (armor ammy belt) and still hit bps, have good damage, and good mf.