I have not explored enough of Cauldros or Sylvalum as of yet, so I feel as if I cannot provide a fair answer.
All the continents are amazing though!

I will give an answer when I feel as if I have spent enough time with the game to provide a more justifiable answer. 90 hours in and the fact that I have not spent enough time with the areas in this game says a lot!

Huh?

Is the image not displaying correctly?

Yeah the sylvalum image is blurry.

But Sylvalum is my favorite continent. Though the Divine Roost in Noctilum is my favorite area of the game.

Yeah, as stated above, it's quite blurry. 

That's weird, I'll try replacing it with one from a different site.

Speaking of which, maybe I just suck at searching, but it seems really hard to find a large, high quality pic of Sylvalum. :/

Is it better now?

I like Oblivia most personally, just found it most fun to explore.

Can't pick yet...

I like them all for different reasons. Primordia is a great first continent with a combination of the familiar with the alien and a really awesome sense of scale. I mean all the continents look big and are big but I think Primordia really sells it the best next to Noctilum. Noctilum's bioluminescence gives it a great fantastical feel and is a perfect "second" area as it elevates the alienness of Mira more. Also, the music in Noctilum is pretty freaking awesome. Oblivia also brings some great music and a lot of mystery to it as well with all the interesting ruins. And while annoying, the EM storms are cool to see. Sylvalum also has a lot of mystery and intrigue but of an entirely different kind. It's the most purely alien continent of the lot, with weird creatures and plants even by Miran standards. The music is also great and really sells the intrigue. Haven't been to Cauldros yet.

If I *HAD* to pick one, I would say...Noctilum I think. For the coolness but Primordia is a close second.

Definitely Sylvalum. It's a tree that dies and decomposes, which brings in a variety of species, how awesome is that?! it also offers enough space for skell driving, and two out of four of my favorite chapters happens there. When it's night time, the glowing sight with the music...

I went with Noctilum, but if you ask me even just a little later today, it might be Sylvalium.

It's a difficult question, because I like all of the continents so far except Cauldros, and only because I haven't explored much of Cauldros.

Noctilum, I haven't visited Cauldros yet but since I really hate lava/hot weather it won't change anything.