Heavy bag?

I'm getting a heavy bag soon but which material should I get out of these two; vinyl or canvas because I haven't got a clue, suggestions would be grateful. Thanks.

in the olden day the canvas bags were rock hard, but nowadays the material is irrelevant. the brand and weight are more important

but personally, id go with vinyl since you can do very light work (like shadow bxing) on it without skinning the knuckles.