This is actually a very interesting question. Both methods have their own advantages and disadvantages, so it depends on what you’re trying to achieve.
Using time dilation in Sequencer is easy to use, you can easily control the speed of the entire sequence. But as you mentioned, you have more control over individual elements within the sequence, including Niagara effects when making the animation slow-motion.
So I’d say it depends on the necessary requirements for the project.