I prefer the harlequins too, but when they finally reach 2"+, they kind of look out of scale with a 10g. I feel like they're too big in my 20. granted, they have plenty of space, I just wish they stayed smaller.
My son has 10 of these and the way they shoal is amazing they are great little fish but if i had to choose between black neons and harlequins i would go with the harlequins.