LTSpice has benefited from a full time developer and a large number of users for decades. Linear and later AD have test equipment to characterize ICs and validate models that we can only dream of.
Ngspice has a lot of catching up to do, but i is worth it to get control. As an example, LTSpice recently removed a load of obsolete jfets from their library - the sort of thing the DiyAudio crowd would be likely to want to use in simulations of vintage circuits.
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