Both are good for rebuilding and I own both. I personally don't generally rebuild on the Zephyrus, though... it's smaller compared to the other solutions Youde has. It has a purpose, but I'm not a huge fan of rebuildable coil decks. I generally prefer a dedicated rebuildable
tank to a rebuildable screw in coil deck ... there's always, ALWAYS tons more room to work. Insofar as rebuildable decks in clearos go, though, the Zephyrus is interesting. You actually use a different base and rebuild on it... the rest of the tank is still designed for the tank to work as a standard clearo, though, so the deck is slightly tinier. The Goblin V2 and Goliath V2 have tons of room to work with.
For UD's (Youde's?... whatever...) RTA's, the Goblin Mini is my current favorite. Easy to work on (Goblin V2 and Goliath V2 are still easier, though), and it hits like a freight train... flavor country. Supports single or dual builds, small profile, and has a 3ML capacity. It's been my go to RTA since I got it. The only drawback is that I have to use the (included) 510 adapter to use my own drip tips. No biggie, though.