I would vote for oregano. Although thyme and oregano are about equal medicinally, oregano has a more vigorous growth habit and can grow as high as 18". Thyme is a low creeper, rarely getting above 6', with much less biomass in its stands. Oregano also crowds out weeds better. Mine is even taking over from the centipede and Bermuda grass in the lawn.
Prune tall rosemary varieties, bay laurels, lemon verbena, ect into small tree forms and you could have a lower growing herb right up to the base and get double use of the space. I think there are actually many shrubby herbs.