Personally I've been someone who avoided girl groups for a lot of time.
Then 2NE1 happened. And Orange Caramel.
I don't like most girl groups' music, outfit, concepts and singers. They are often too much one like the other and not really special.
With boy group is the same, and that's why I only watch some idols, because then I get bored.
For example there are tons of young boy groups better than the SM ones, probably even of SHINee, but I'm lazy and I don't care enough about kpop music in general to look for them. Sometimes I stumble upon some boy group and realize just how unfair the market is, but Key is in SHINee, Tao e D.O. are in EXO and I have all my SuJu biases.
I tend to prefer watching boygroup because even when the music is bad or boring they have more enjoyable choreographies (EXO's Wolf, horrible music, awesome dance I even watched it with mute on).
With girl groupsI often can't stand the music nor the choreo. It can be alluring, but I prefer to watch something cool (2PM, GOT7, Amber, BoA). For this reason I don't really like Big Bang. They have little choreo, and they're not my kind of music. Their music has more quality than a lot of other boring kpop idolish music, but it's not what I'm interested in. While I LOVE GD. And for his music. Nothing like 'Oppa have my babies', that would be BoA if any. Ops, but that can't really happen.
BoA was cool, I suspect she's trying to modify her image, but she was a very cool performer, more classy, powerful and interesting than a lot of doll like, all cute and dumb/innocent girl groups.
All in all I think girl groups tend to rely more than boy group on image and miniskirts or outfits. Boys too do it, but they do it being cool. In girl groups I'm sure a lot of them can be very cool, entertaining and charming, but I often get bored because they have to behave. Too powerful? You're acting like a man. Too straightforward? Same. Mini skirt? You're so feminine, national sister, role model of the doll like girl. And it makes me mad, because they train a lot, with different kind of music, dance styles... and then all they do is swaing hips, making eyes, and sensual hands/arms gestures. (Let them) DANCE FOR REAL!
Also and this is something I finally understand, older idols, and especially male older idols, are more free to be less idol-ish, and that's why I have a thing for older idols (including Hyori, she's great!).
It's ok, idol world is full of plastic, figurative and for real, but among all the bad music and not really great singers I'd rather have fun and care for the few people I really like as performer or artists.