My pheonixes, naked necks and Cornish bantams are my go to birds. But the only one of those you might find in a store is the NNs. Pheonixes (not mine though for what ever reason) that are duckwing (silver or gold) will show males by 5 or 6 weeks because of feather color. If not earlier by comb...
I guess it just depends on what's available since you mentioned a store and not a hatchery. What I would recommend almost never are sold in feed stores