Defender

Defender but if you know anything about what you are doing you can use striker, it's good for playing defensive as well

Defender is the better subclass for PvE in most situations, especially while you're under geared for things. Once you're geared out running end game missions, it then depends on your play style and who you're playing with. Defender with Saint 14 is generally considered the best setup for an end-game Titan, which I agree with to an extent. If you're playing with random people or people who don't have good situational awareness, this is absolutely true. If you find a regular group of people to run with who are good players and are responsible enough to keep themselves alive and not die to stupidity frequently, Striker is the better option. The damage from FoH is second only to Nova Bomb for PvE, and flashbangs are the best PvE grenade in the game for end game. It's equal to a Saint 14 blind you can put where you want with a faster cool down and it doesn't use your super.

Just put all your bounties into it but don't actually use it til you got a row or so done

Defender only if u got saint 14

I'd say finish leveling your striker class first, then work on finishing your defender class. The defender class has more armor overall. It also depends on your playstyle, as striker, you can use the super to wipe out large groups. As defender, you can gain armor or weapon buffs through super (Coupled with the Saint-14 you can blind enemies that come through your bubble). It's good having both fully leveled so that you can swap around when you need to.

Bump

with striker you get kills, but with defender its a protective bubble but also provides support to your teammates