Looks good both ways, although you do say the flat top if from several years ago ... so if you have advanced balding since then, the sly option might now be a better choice.
The Sly look, I think, is a bit bolder. From my own experience, the sly style feels much better. Smooth on top. And it's easy for me to keep it that way rather than the need to go to a barber shop.
Being BBC for over 5 years, I'll chip in for sly, if you're asking for an opinion.