When comparing Quicksilver vs Notational Velocity, the Slant community recommends Notational Velocity for most people. In the question“What are the best power user tools for macOS?” Notational Velocity is ranked 11th while Quicksilver is ranked 16th. The most important reason people chose Notational Velocity is:
The interface is clean and unobtrusive.
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Pros
Pro Easy-to-understand noun-verb paradigm for creating tasks
Pro A lot more powerful than Spotlight
Pro Makes it really fast to do a lot of actions
There are customizable triggers and capability to execute multilevel commands - e.g. launch terminal app, give the location of script and supply parameters for the script with one command.
Pro Vast extensibility via plugins
A lot of different plugins for browsers, file systems, mail clients, etc.
Pro Simple and minimalistic
The interface is clean and unobtrusive.
Pro Free
Pro Syncs with SimpleNotes or Dropbox
Cons
Con Feels a bit outdated
The last release was from 2011. Although due to its brilliant simplicity in doing what it's designed for, some might think there hasn't been any need for an update, as long as it still works with the newer OSs.