FabFilter Pro-G is the best gate I've ever used.
However, when I reach for a gate, I'm often thinking of some specific tasks I'm trying to do, and a gate is usually just one step for some other goal. So for some tasks, I'm starting to like the Waves eMo D5 Dynamics plugin of all things, which has an interesting configuration of 5 different dynamics processors in one, and they essentially work in parallel with some nice tricks, so you can achieve some very useful results that you wouldn't easily arrive at with other plugin combinations, and I like that's it's zero latency, very clean, and CPU-friendly. Perfect for some tasks. The individual algorithms are not necessarily "special" since they are not trying to emulate anything, but the combination together lets you look at tasks differently (including just gating by itself), and provides a useful extra tool in your arsenal.