1) Christopher Reeve : he just had that X factor that made him both likeable and believable, both as the Man of Steel and Clark Kent.
Even as the Superman films got successively crappier, he stayed great, and was good, no matter how awful the movie - he was the one good thing about Superman IV.
I mean, if you think about it, Superman the Movie has one of the lamest resolutions to the final problem of any Superhero films (he flies really really fast around the world, and it turns back time ?) but still we love the film.
Maybe it's because I saw it when I was 8 and can't let go of the nostalgia, but regardless, Reeve's still my favourite.
2) Henry Cavill: A very very close second. A different version of Superman, and one I really like. I think Cavill did a great job with it, but for whatever reason (you could say the particular characterization didn't give him as much to work with, but I think that's a cop out, we have to accept that this was a different Superman).
Anyway, for whatever reason he's not quite on the same level as Reeve. A very good Superman indeed, and the right man for the job in Man of Steel, but there's just something special about Reeve that I can't put into words.
However, having said all that Cavill is the closest to the look by far. When he stepped out wearing the suit for the first time, I said to myself "That's Superman!" and his performance was very good overall.
I'm expecting great things from him in B v S, as he becomes more comfortable with the role.
3) Tom Welling: Never really liked Smallville, but he did the young Clark some justice.
4) Dean Cain: Not really a Lois and Clark fan, but he was a solid, likeable Superman.
5) George Reeves: back in the day, he was definitely a good Superman.
...
and in last place by several million Brandon Routh, a truly lame performance as Superman, nothing Super about it. Just because he bore a passing resemblance to Chris Reeve he got the part...but is that Bryan Singer's fault, who knows ? Anyway, he was a terrible Superman - I would struggle to find a less enjoyable version of Krypton's last son. (even the voice actors were more compelling !)