I think that its difficult to advise you on types of mulch since i don't know your climate, but where i live (wet summers and wet winters with some freezing) i have used Cocoa hull, gravel, regular an some lava rock and pine needles.
For all the options mentioned, they work all more or less the same. Maybe the lava rock was a bit better in keeping the weeds down, when it comes to economics i would highly recommend the pine needles since they can be picked up for free also the drainage is pretty good. The cocoa i don't use anymore, it does not look very natural and if your cats or dog eat it it could cause a problem.
The gravel works well, but its not free, so for me the pine needles are the big winner.
Finally you could also consider filling the leftover space in the pots witch small ornamental plans or mosses, it looks more natural and essentially makes small micro gardens.