I'm in the "Joffrey was a POS, purely evil character" camp...
He's not like Jamie who has some redeeming qualities... Most seem more complex, but for me, Joffrey = Caligula, from the in-breeding to the sadistic nature, to the tantrums and quick temper.
There are worse though... That's kind of what always comes up in TWD too, that there is always someone worse.
But watching Joffrey croak was pretty damn fun, I have to admit.
Long list of suspects too... Tyrion's about the only one I don't think would've done it, ironically.
This certainly changes things... I've not read the books so I don't know exactly who the Lannisters would attempt to replace Joffrey with then... I know all the people who could make claims, and I'm probably forgetting a few of them even, but who would the Lannisters try to put there? The marriage isn't really official, so it's a dilemma for them. Cersie would probably be the most likely to take the throne for now?
It's nice to hear it stated that basically the Starks aren't out of things, by the way. That there is the thought people would rally to even a young Stark being alive if they knew. It's felt like, to someone who hasn't read the books anyway, that they're pretty much on the fringe of the game at this point.