It depends on what you want to achieve with your writing goals and target reader.
I will say that Webnovel is easier to get reads if you're willing to pimp your book a bit. Just remember the rules for shameless plugging on this forum.
I'm still active on both sites, but Wattpad is definitely harder to gain readers than here for me. So I don't write there anymore. Great features and support, but with no readers makes the story sharing pointless.
Having said this, for me, Webnovel has seen a small improvement in readership for my work, but I wouldn't say WN the best for niche, experimentive stories or less known categories.
Another constant struggle I face on this site is where a large chunk of readers for my genre bypass originals altogether.
As far as popularity goes, both sites seem to thrive on similar genres where fantasy, system and romance are big hits.