I always regard whatever says I'm faster and ride farther as being the most accurate.

FWIW, Cyclemeter for iPhone always showed my times as faster than Strava. Never compared it with a bike computer. I didn't get one until recently, just a $12 generic wireless speedometer to save a little weight on the front end compared with the iPhone and mount. Smartphone goes in my jersey pocket and I usually don't even look at it until I get home.

And my cheapo bike computer usually agrees with Strava, Wahoo Fitness and others. Not much real difference between 'em.