hey the title says it all... deepbit's speed says "292MHs" whilst guiminer says "270mhs" which one is more accurate?
With most pools, your reported hash-rate is based off of shares over time. GUIMiner reports the 'actual' hash-rate.
If the pool is reporting a higher hash-rate than what your 'actual' hash-rate is, you're getting 'lucky' solving each share. This is normal variance.
Cheers,
Kermee