I don't really have one I watch more than the other. Going through the list:
Leora/Paul: pfft
Lora/Max: I watch them more now that they have a mic in the living room. I like the fact that they seem to have a nice stable relationship.
Alina/Anton: I watch them despite not having a mic, but only when Alina is lying on the couch in her underwear or if both of them are in the living room in the hopes that they fool around on the couch.
Maya/Stepan: I don't watch them that often, but this is one of my favorite couples.
Nora/Kiko: I don't watch them that often. They seem quite boring and I don't really see the appeal in Nora.
Isabel/Marcelo: I used to like them when they were in Alma/Stefan's place, but now not so much. There's something off about them that I can't quite put my finger on. She likes to fuck but I get a serious lack of chemistry vibe from them. It's almost like they're just going through the motions.
Alma/Stefan: I used to watch this couple the most, until they got engaged. Now for whatever reason I don't really care about them anymore. I still think Alma is super hot though, more so than the rest of them.