I've lived on the Holloway Road, then bought a flat in Islington, then moved to a house in Greenwich and I also once owned a small flat in Charlton. (Also prior to all this lived in Turnpike Lane and Ealing Briadway) so I think I can speak with some insider knowledge.
Without a doubt I'd put Greenwich first - it's pleasant, green for London, fabulous park, near the river, brilliant weekend market, good transport links. Islington is also a great place but I'd say less so for families, terrific for singles, young professionals and/or couples - it's more "urban", more buzzing and more pricey I think (although depends exactly what bit of Islington you go for versus which bit of Greenwich eg east of Greenwich park is more expensive than west....and probably on a par with expensive bits of N1). I thought Charlton was not so good and Holloway similarly seemed to me quite grubby and very inner city - don't want to offend anyone who lives in either place but if you can afford SE3 I'd go for it.
Then again every place has its own plus and minus points, and if you find a good property in a good bit of any of these 4 places you could still be very happy.
But Greenwich, yup, it gets my vote.
PS I got married in the Queens House in the park. Overlooking the naval college. Many happy memories.