I have not had great luck with any of the creeping thymes in the Pacific NW, and I've tried quite a few. The best one for me has been
Red Creeping Thyme (Thymus praecox 'Coccineus') which stays evergreen if a bit sparse in the winter, then puts on fresh growth when the weather warms up. Most of the others tend to die out in the center.
An alternative you might consider is
Smooth Rupturewort (Herniaria glabra) which does stay evergreen, spreads nicely, and seems to be hardier (for me) than thymes.
