OK, so another voice is heard (I'm not the different than some here though) here is was I say.
Tapas has a lot more creator friendly features. That said, the audience seems to be smaller here than there.
Webtoons likes regular updates and will effecting reward you. At least once a week (with 24 hour leeway I've noticed) is good to maintain and grow your comic.
you can save a draft of the comic and then publish them in the order you saved them. I do it a lot and can easily pop on the web and have it uploaded. Auto upload seems to be reserved for the featured comics (contracted) only.
The size restrictions are not that different than Tapas, but you can upload more files (100 I believe to tapas's 40)
overall I am happy with both though it is frustrating they are only just now starting the e-mail the creator bit for comments.