A 15 gallon pot will comfortably hold a 4 or 5 foot tree, and a 30 gallon tub will support an 8 foot tree. Wooden boxes and barrels, ceramic troughs and pots, and decorative plastic can all make good containers. Wooden containers are attractive and affordable, and if they are properly made can last for many years. They should have several holes in the bottom for drainage, and be either banded or doweled in the corners for strength. Beware of those made with nails or staples, they will fall apart very quickly.
Ceramic containers are also a good choice, but a large one is very heavy.
The glaze color of ceramic containers should be compatible with the color of the tree, and not so bright as to compete with the tree for attention. Most economical, perhaps, is a plastic pot, and attractive ones can be found. Casters on the bottom of large pots and tubs will simplify moving. I shop for containers that are wider than tall because they are far more stable, and I enjoy the aesthetic of a larger soil surface for ground covers, dwarf bulbs and rocks, driftwood or other decorations. The soil used in container growing is very important, especially since there is so little of it.