The Twilight Zone theme or the X files theme?

The Twilight Zone. Though with Catman's life, the Munster's theme is far more likely to be played.

TZ, as homergreg said, it's so ubiquitous, it's likely to start running through my head anyway if something really weird happens.

Although TZ's intro was changed up a few times, I think the whole thing is better than the collage of weird stuff that X Files puts up. Especially with the Serling voiceover.

TZ's "Doo-doo-doo-doo-doo-doo-doo-doo" has been ingrained in my head since early childhood.

The Twilight Zone

I like both pieces of music and actually prefer the TV series THE TWILIGHT ZONE over THE X-FILES, but as for what piece of music is more likely to play in my mind when something strange or weird happens, I'll give it to THE X-FILES.

Theme from 'A Summer Place'

The X-Files theme playing whenever something weird happened would be very cool.

The "Twilight Zone" theme has actually taken on a life of its own to the extent that people might hum or whistle it when something odd occurs.  Not sure that anyone does that with the X-Files theme, which is just kind of a Doctor Who theme knockoff, after all.