Guild Wars 2

I’m running a nice Knights 0/0/30/30/10 GS/Hammer build, and I’m finding it simple enough. However, I’m continuously debating in my head whether I should fill my third utility slot with either Endure Pain or On My Mark: On one hand, On My Mark is very useful as a third shout (increasing my shout-rotation’s healing by 50%) and with my Soldiers runes also removes another condition; but endure pain is such an amazing ability against anything that can burst you down such as Lupicus’ bubble, bad positionning in dredge fractal and knockdown situations.

I’m currently running the trait that also activates an endure pain at 25% life.

Any idea which I should take over the other? Is there any definite set of pros/cons or is it just preference?

I say, if it works for you it’s good. Play some time with both skills.
For me EP is far from amazing. Situational, short duration, long cd. I am using it sometimes, but rarely.

What Liltaro said, but you could always just switch the skills based on your situation.