TBH I Like shattered observatory too. It is fun and (Imo) isn't nearly as bad as thaumanova reactor or aquatic ruins.
I'm hard pressed to pick a favorite. Mai Trin is super straight forward and rewarding. I also like Twilight Oasis and Urban Battleground. I would like to see more fractals where you get to play as different historical events so thus far I'd have to say those are my favorite.