What are the quickest moves to use to rushdown?

[Nomzr]

I find myself inconsistently performing rushdowns. They usually end on a sweetspotted up-special or dair, sometimes, although rarely, bairs. A lot of the time I get interrupted, and I assume this is because my moves don't come out fast enough to counter the other's move, which comes out much faster allowing them to break my rushdown. What are the moves that come out the quickest, thus allowing me to get them hit-stunned again instead of allowing them to break out and do something with a faster move?

 

[cisyphus]

Nair seems infinitely better, but honestly I don't see why you can't just poke with back air and forward air and provide safe pressure that way.

 

[-Sothe]

I rush down a lot, and my standard sequence is to short hop at them, throw a razor leaf, and see if I can't catch them in shield. If I do, I full hop, fair their shield, and come down with a nair. In general, full hop fair into falling nair is really good for pressure (but only if you land behind their shield). You can also approach with RAR bair and try to follow up into nair, grab, or f-tilt if you like.