Try them both and see which works best for you. If you go with the Weber kettle bottom, might I suggest cutting out the bottom of it for better airflow and allow the ashes to fall to the bottom of the drum? Here is an 18" Bar-B-Kettle I drilled a ton of holes in.
It worked fine, but if I were to do it over, I'd cut the bottom out below the grate.
Here is another basket similar to the square ones of yours. It is 12"x12"x12". A little lighter than yours but it works just as well.
Looking at your fire baskets, I'd use larger expando on the bottom.