Serum is lightyears in front of the other synthesizers, however understand that specialized capacity isn't by and large the essential concern. You could discover freeware that achieves the vast majority of what all these synths do. In any case they all utilize their own particular channels, they all have their own voicing calculations and strategies for detuning and they all have their own sound, because of being totally different softwares.
When I see comparisons between these 2 softwares I frequently feel like the inquiry is to some degree like asking "tenor sax versus baritone sax, upsides and downsides of each?" Well, they work in basically a similar route, they differentiate each other in workflow, and they have an exceptionally similar sound. One fits a more profound, hotter quality while the other characteristically has flavor to it.
I find that Sylenth sits in my tracks effectively. I find that Serum can deliver some intriguing music and tonal advancements, and special sounds. Yet, Massive still sounds dirtier, more profound and heavier than any synth around. It's simply the characteristics that the synthesizers forces, so it's best to tune in to recordings and choose what nature of sound you are after, as opposed to chase for specialized particulars as I would see it.