I think neons and cardinals are overrated! They are nice to have in a tank for a splash of colour but no matter how long I sit and stare at them, I cant force any personality into them! And they only loosely shoal at best which is frustrating, they don't much swim together once settled.
Mind you, kept in a tank with a schooling species of tetra, they look great
Would love to have a shoal of 60-70 Copper Harlequins, Harlequins, Gold Tetras or Silvertip Tetras and then a shoal of 30 Cardinals to add a splash of colour. And for the top of the tank I would want a shoal of 15 or so Silver Hatchets (healthier, stronger and slightly larger than marbled) and a nice big shoal of Skunk Corydoras (C. arcuatus I think?!) of maybe 20-30 cories.
That would look epic, covers top (hatchets), upper middle (schooling tetra), lower middle (cardinals) and bottom (corydoras) and of course, can have a few pairs of this and that knocking about, dwarf cichlids and the like. I might have been tempted to have a group of 6-8 Yellow Honey Gouramis for the colour. All the above species can be swapped about but you get idea).
Actually, I quite like the idea of heavily planted low maintenance (low light, low ferts, low maintenance) tank with a shoal of microrasbora! About 300 of them! Lol
would look epic! Not to mention cost a fortune lol but I am sure shops would do deals. I had a guy buy 50 cardinals off me the other day and I know the last time I saw him he bought 100 cardinals. He has a tank of a similar size and in the photos, it is stunning!