Just typing this out to get a grip on my fandom...
AKB48: Most exciting time was in 2009 when the rise began. Great singles, lively, fresh. Budokan concert was epic and they managed to stay on top of their game all the way to Tokyo Dome. After that the group feels shattered, in the sense that there isn't a feeling of unity anymore. Many cliques, lack of interaction. My biggest issue has always been the 9th and 10th gen (AKA Team 4). I never really bonded with them, but that's ok. The problem is that they don't interact with the others, something which became painfully clear in that AKBeats segment on AKBingo a while back. What's the point of shuffling the teams over and over again if the girls don't make new connections. Furthermore, I feel they get an disproportionate amount of screen-time, especially compared to their senpai (i.e. Sumire, Aamin, and even Fujie, Tanamin, Chiichan, etc etc). Lately the shows have become better and the new single looks good, so yeah, can't complain too much I guess.
SKE48: Always felt connected to them since this is the first J-pop group I followed from the beginning. The Nagoya Ikki performance late 2009 turned out to be their peak... A lot of the amazing girls from that era are gone (Shinkai Rina, Matsushita Yui, etc) and the performances were just fierce. Great singles and stages as well. When the third gen join I was a bit weary but they turned out fine (Akari, Yuria, etc). However, current SKE48 seems like a totally different group than the one I initially fell in love with. Severely lacking in (future) star power, singles with less impact and the dancing doesn't stand out from their sister groups anymore. Hopefully the shuffle is the beginning of the rebuild of SKE48 2.22. However, when it comes to SKE48 I'm just of those fans who clings to the past, always remembering the glory days.
NMB48: Epic start with a great agency and nine regular TV shows. A recognizable sound. two aces right from the start. Great! However, the group is tormented with graduations and a lot of the cool shows are gone. Still plenty of potential and star power. I like to think we haven't seen the best of NMB48 yet. As a group I never bonded with them as much as SKE or AKB. I didn't like the way they promoted the group at first and the owarai and kansai-ben gets a bit tiring after a while.
HKT48: Horrible start, but after a major clean-up they have captured the hearts of fans in rapid pace. They're still lacking a clear center/ace, but at least there are a lot of girls who qualify for the spot. The girls can make a show as simple as Odekake into a great watch and that's important. My main issue with the group is the amount of kids, some even post-2000. I know it's the way it goes, but for me it makes it hard to get into. The amount of super young kids will only increase over time (Team T, etc). However, for now it's probably one of the most enjoyable groups.
Nogizaka46: This is a tricky one. When I watch the show I usually enjoy it. However, they lost me quite early on when all most the girls I liked didn't make (TV) senbatsu. The second thing is that their music doesn't appeal to me. That's probably the biggest issue. The girls are all pretty entertaining, even though I don't have any favorites I'd actually want to collect pictures of, etc. So yeah... perhaps it could have been one of my favorites groups if things would have gone a bit differently when they debuted.
Conclusion: If I complain about the present it's only because I loved the 2009 era so much

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