I recommend the minimum size pot that allows you to dig up the intact rootball and still have room for new soil around and under it. I don't grow these three but I do have a sizeable number of minis in containers.... addictive little stinkers. My largest containers are whiskey barrels and smallest are 14-inch. Anything smaller than 14-inch I only use for moving minis up or to put into society raffles, not permanent plantings. I don't have any micro-minis.

I have my second year minis in pots.
http://i153.photobucket.com/albums/s218/joet1485/sawhorse5.jpg

As you can see these are three gallon pots. Five gallons would be better but either will work nicely. Be sure to water them every other day unless it rains and you should be pleased. All my minis are in pots except red cascade. I can cut six or more a day as cut flowers usually but now that the heat in upon us they are very small and not so good as spring or fall flowers.

I put my new mail-order minis in either 10" pots, moving them up to 12" when their roots have filled in the smaller pot, then to larger pots still, depending on how vigorously they seem to want to grow. But only the smallest of small stay in 12" pots. Most end up in anywhere from 15" to 18" pots. Some minis are vigorous enough to even fill out 20, 22, or 24 inch pots, but I try to stick to a size I can actually move myself without fear of getting a hernia. Generally, 15 or 16" pots works well for me for any bushes that stay below 2X2 ft. The larger minis get 18" pots. (I'm talking about diameter, of course.) All my roses are in pots, by the way.

One more thing about pots. Because the weather gets so hot here, I avoid clay pots like the plague. Unglazed clay pots allow evaporation too quickly and can end up baking the poor roots. I have a couple decorative glazed pots that were given as gifts. But even glazed pots hold more heat than simple plastic, so to use them I slip a plastic nursery pot inside the decorative pot and fill it in with pine bark mulch for thermal insulation. That seems to have solved the problem of "baking" the roots, which I used to see. Best of all are the rigid foam pots, but they're so darned expensive. Basic plastic works.

I put my full grown mini's in 5 or 7 gallon pots and that seems to be a pretty good fit for them.
John

Important not to use too big a pot for a small plant- the soil will get compacted and sour before the roots fill it. Better to move up a size or two and then repot six months or a year later when they have grown.
Try a six inch pot for a small plant and then move up to 8 to 10."