Haeundae I-Park and Zenith are legendary
Mokdong Hyperion 1st (2nd is ugly)
Tower Palace (I don't think the 3rd one is a big deal)
Songdo Senpak The Sharp 1st and 2nd
Raemian Chalitus
Acro Seoul Forest (Galleria Foret next door is not so great;;)
It's just a personal opinion
Feel free to talk about it as much as you want haha.
If you have any other pretty apartments, let me know.