I used to love harlequins, but since getting pristella's i have decided they are now my favourite. Beautiful to watch, not scared of anything,bigger than most tetras, and are always shoaling.
Pristella are beautiful, i have them and pork chops in the same tank, and they're both great shoals. The other i'd recommend for planted tanks especially is ember tetra- gorgeous little sparks of gold
Spotted silver dollars - look better than regular silver dollars, stay smaller but are just as active. Though exodons and galaxy rasbora come a close second/third.
Got to be harlequins, ever since most of mine died i have been umming and arring wether to replace them, but i am going to get a full strengh 10 when i re-do my tank soon