In the long run, A-rank for weekly would be best.
On those you can at least get in a few hits/spells before they're dead, actually giving you a chance to get enough contribution.
In the long run when less people are doing the hunts, A-rank is easier to get people for. Of course, by then it might be more worthwhile to actually go down to B-rank for the weekly.

The daily marks need a buff in how many allied seals you get though... 7 a day, and that's supposed to be for casuals... meaning 5 weeks to get enough seals to buy one book towards sand/oil... rewards here should be increased so that it's possible to buy one book per week.