Welcome to the character rankings, we begin with Keroro Gunso, but as this series is absolutely ridiculous in length the ranks will cover the first few characters with more added at a later date.
Sgt Keroro is incompetent at his job and ultimately fails at invading Earth, his plans all fail, yet is perfectly content with living in the Hinata house, reading manga, surfing the net and building Gunpla kits. His energy can relate to a lot of viewers.
Corporal Giroro is the serious one but has a strict code of honour, he falls for Natsumi after she decimated his traps. He's generally the one who reminds Keroro why they are here. His comically serious routine can be fun to watch.
Private Second Class Tamama is the wide eyed young subordinate, idolizing Keroro and generally going along with everything but has a hidden temper manifesting in a large mouth beam. I thought I'd hate this character but his wide eyed innocent persona grew on me.
Fuyuki Hinata is a young boy with a hobby of occult and unusual, he was first to accept Keroro and acts as audience surrogate but there's not much stand out in his character.
Natsumi Hinata more than makes up for Fuyuki's lack of personality, she takes no bull from any of the Keronians and already I can hear her dub voice and I've not even seen the dub. To be honest liking her depends on if you like the actress Cherami Leigh a.k.a typecast as the victim of the crazy shenanigans, very much love/hate.
Aki Hinata doesn't seem to mind the whole alien frog business as being a boy's manga editor she can draw off their strange culture, doesn't like furry animals based on some really off putting dialogue in episode one but I still like her for very different reasons; don't look at me like that, I'm in my 30s now and my waifus tend to be more mature and she's a biker.
Momoka Nishizawa is a rich girl with a one sided crush on Fuyuki, an old concept but mixes well with her split personality, the normal side is timid but her other side is borderline crazy tempered, situations involving her can be fun at first but don't have ever lasting appeal so her routine does get old.
Keroro 7.3/10
Giroro 8.8/10
Tamama 8.2/10
Fuyuki Hinata 6.3/10
Natsumi Hinata 6.7/10
Aki Hinata 8.2/10
Momoka Nishizawa 6.9/10
This post will continue at a later date