Florist mums are annuals found in the floral department of grocery stores normally wrapped in pretty foil. They are indoor plants grown to be given as gifts, not to be planted outside.
On the other hand, garden mums are grown to live and thrive outside. They are the kind of mums you can plant in flower beds and containers on your porch. Garden mums will come back next year.
If you want instant curb appeal to wow your guests, pick a plant with lots of fully opened blooms. This plant will only be in bloom for another week or two, but it will give you maximum impact for a special occasion.
For longer bloom time, buy your mums in late September or early October and buy ones with lots of tight buds that have not opened yet. These have a good 3-4 weeks in them. Maybe a little more.
The stems on mums can be easily broken, so pull the mum out away from its neighbors and check for broken stems. If a stem is broken the blooms on that stem will never fully open.
Avoid plants with wilted and droopy-looking areas. This can simply mean the plant has not been watered enough or it could be a sign of a nasty fungus called Chrysanthemum Verticillium Wilt.