would go with the blue acaras. convicts would definitely be out since they are such prolific breeders they would soon overrun a 40. jewels are nice, but like cm said you could have a trio of one species. i would go with the blue acaras since their colors are much more stunning than the jewels.
dw. just a thought. Ive been thinking bout the 4ft tank im getting and its crossed my mind that i could have bearded dragons (lizards) instead? ive been wanting to get some but not sure what to do yet!