Oh I’ve listened to dozens of Kpop girl groups so I think I’m qualified to answer this 🙂
My top 5 and I’ll give reasons for each
1) Red Velvet
The more I listen to them, the more I realize how talented they are and how deep their catalog is. They are very musically versatile – they have 3 main types of songs they do – the upbeat poppy kind (Umpah Umpah, Red Flavor, Queendom), the slow ballads (One of these Nights, Wish tree), and the R&B (Bad Boy, Psycho, Automatic). Since I love R&B, Red Velvet is probably right alongside Wonder Girls in having the deepest R&B catalog out of any girl group. Not only that they are all great singers even the rappers (Irene & Yeri) and their visuals are all stunning as well (Irene as we know is one of the great Kpop beauties). Wendy is a singer who can belt out songs on the level of Taeyeon as well. Due to their musical diversity, talent and longevity, they are my favourite Kpop girl group ever.
Just like with RV, you have to dig in deeper to Apink’s catalog to truly see how great they are. They are well known for the cutesy upbeat pop songs like Love, Mr. Chu and Nonono, but they also have a R&B side with songs like Deja Vu and Promise U as well. The are also vocally talented enough to appear on Killing Voice. I value musical diversity and talent so APink is pretty high for me.
People who listen to Mamamoo know how musically diverse and talented they are. They are one of the if not the best vocalist Kpop girl group of their generation. Solar, Wheein and Hwasa can belt out solos like no other (prime example is I Miss You) and Moonbyul is a very good rapper. They can do upbeat tempo songs like You’re the Best, Hip and Egotistic, jazzy tunes like Piano Man, slow R&B like Morning, sorrowful ballads like the aforementioned I Miss You, etc they are probably the most musically diverse Kpop girl group I know, but they rank a bit lower than RV and APink for me because I just think their songs are overall more catchy and have better hooks, but Mamamoo is up there for sure.
4) Girl’s Generation (SNSD)
THE Kpop girl group of the 2nd gen era, SNSD brought a renaissance to Kpop girl groups in the late 2000s. Although not every member is equally talented (Taeyeon for example is by far the most well known vocalist), they have a very solid catalog of songs. I would say their strength is in the uptempo pop songs like The Boys, I got a boy, Gee, Mr Taxi, Genie, Hoot, Lion Heart, Oh etc and the slow ballads (Light up the sky, How great is your love, Star star star). So while not as diverse as the above groups they make up for it in quality and quantity in what they are good at.
Surprised? This group may not be that well known, but they have a very good catalog of mostly uptempo pop songs and some slower R&B ballads. For a group full of stunning visuals you might not think they are as vocally talented as they actually are. But songs like Feel Good, DM, Stay this Way, Weather, WE GO, are infectiously catchy, paired with some great slower ballads like 0g and Starry Night. They might not be super well known but they are one of my fav girl groups for sure.
Honorable Mentions to round out the top 10 – Wonder Girls (they are queens of retro R&B style), TWICE (they do the upbeat pop thing really well), Girl’s Day (a surprising amount of solid upbeat pop songs and ballads), AOA (more than just sexy looks, they have a fairly deep catalog of diverse songs too), SISTAR (Hyolyn’s R&B and Soulful vocals is the star of this group for me)