Both are nice semi-dwarf (8-12+ft.), upright selections.
Grown in a small pot, they will probably not attain the height that would be possible in the garden, because of root containment.
Other options would be; Dwarf or Minature cultivars (2-8ft.).
Some weeping cultivars are also available.
Here's a link to TAMU with a litany of cultivars, but many are relatively difficult to find.
Whatever you select, Good Luck!
Rb

Here is a link that might be useful: Crape Myrtle Varieties

i picked up a crepe myrtle 'shrub' of some sort two seasons ago. It looks like it's going to bush out and maybe attain a height of 3' and a width of 4'. don't remember where i got it - Home Depot? i think it came from the Prove Winners nursery? at least, i think that's what it was tagged with. i tried to find the tag but didn't have much luck.

Michael Dirr and associates developed a series of dwarf crapemyrtles, at the UGA/CANR facility, Deering,GA, that they named the Razzle Dazzle® Series. They are being marketed as Proven Winners/Color Choice plants by Zelenka Nursery (MI,TN,NC) and likely by McCorkle Nursery, which is adjacent to the UGA site. Both sell to big box stores, as well as to local nurseries. A PW/CC retailer is supposed to be a full line dealer, but when "big bucks" talks...well you know how that goes!
Here's a link to the UGA site that lists the Razzle Dazzle® Series.
There may be other crapemyrtles designated as PW/CC, so this is probably not an inclusive list.
Rb

Here is a link that might be useful: Gardener's Confidence® Collection

that's it! good call, rb!