DSGs have fantastically short shift times... close enough to instantaneous that you can't tell the difference. The issue, however, is that you only get instant shifts because the next gear is attached to the second clutch... try a double downshift and things get as slow as (or slower than) a regular automatic.
And many DSGs have issues in low speed traffic, where the clutches take on a binary "on-off" character. One reason I would never buy a Fiesta dual clutch.
Single clutch autos... as others have said... learn to lift off between shifts and blip on downshifts, and you're fine. Best in manual mode... so you can synchronise these things... leave it in auto and things get very clunky... and shift times get very long.
No-clutch... been there, too... amusing to see how far you can drive in traffic before you're forced to use the clutch pedal...
