I don't know if it's my favorite, but I've recently grown to love the word 'verily'. It verily sounds super formal yet funny at the same time. Especially when it's used on its own. Verily!
Perchance is a good contender for a favorite word, too. Strangely, though, I never use either.
If we have to go with a word I actually use from time to time, it's probably 'sear'. It's just quite versatile when used to describing various emotions and feelings, like
A searing anxiety plunged into his gut like was his flesh stabbed by a red hot blade freshly pulled from the coals of a smith's furnace. The jagged edge of his worries twisted and turned, pulled and pushed, ripping and tearing his insides slowly, surely and seemingly without end. Waves upon waves of pain would radiate through his veins, yet he had nothing to show of it but his sweaty palms, fidgeting eyes and ragged breathing. No proof but his thoughts and feelings, things his anxiety wouldn't let him put into words. Nom!