Promoting your comic works roughly the same regardless of what platform you're on. Generally speaking unless you're being featured by the site, most of your potential readership will stumble across you at the top of freshly updated or via a search, and you'll have to do a lot of the legwork yourself otherwise.
Anecdotally most people seem to have more luck/grow a little faster on Webtoons but that's not universally true- for example my comic ended up haivng ~35% more subs on Tapas and much much more reader interaction.
For most there's no reason not to just try both out though. Unless one platform rubs you the wrong way, uploading to 2 doesn't take much longer than just 1 and you increase your potential reach.