There's no such thing as a slick boxer per se. Boxers have to have numerous skills.

Slick is nice but as well as that we want to see:

Aggression
Strength
Power
Balls
Tactics
Courage
A spectacle thats gonna excite
A complete range of shots
Good footwork
Nice head and body shots
Work on inside outside back foot front foot
We also want to see the boxer out of the ring as

Standing for something we like
A decent human being who builds a fan base

The last thing I want to see is a guy running round the ring getting away from shots - I want entertaining

I think people like slick but generally combined with the other attributes. Bottom line is we want to see a hero not a coward, who entertains and inspires us not runs away - thats why I love Ricky Hatton and I hate Floyd Mayweather