I guess Rögnir would be the easier bet. It depends also on the albums you are listening to and how much you are used to hearing upper mids and treble with full energy and distortion, if you like more sparkle etc. It is brigter, closer to a V and has more fun factor. The hole in the low mids actually help with older recordings like Testament / Low, making them sound slightly clearer. But they _are_ brighter.
In the last days, I used Stealth to listen to everything, and I got used to the sound. Rögnir now sounds somewhat off in the tonality. But...with Rögnir you can experiment with pads for slight adjustments.
For me personally, it is Stealth, as it is tonally very natural and sounds correct. But hearing what the metal only listeners prefer, Rögnir sounds like better fit for a metal listener. Stealth is like listening to music in a well treated room with no reflections, echo. Incredible with acoustic music, vocals etc. Distorted guitar sounds like you have connected your headphone to an AxeFx processor (amplifier simulation) and you are hearing it. Very realistic. But might sound dull, as well.
As I am writing this, listening to Opeth Morningrise on Stealth.