From my humble experience i would suggest (the other never heard of nor kept):
D. microlepis (not very active - loses coloring and patterns as it grows - impressive fish though if you are into toothy fish. Decorating a tank is a must cause by itself the fish is not very impressive ... did i mention messy eater?)
Hydrolycus armatus (while i never kept this one, by looking at this forum, the fish looks quite impressive - very toothy - this one i would keep ...my next project)
Potamotrygon motoro (this one is on my list to get but need another top swimmer to balance the look)
P. motoro 'marbled' (ditto)
Polypterus endlicheri (i have this one or a delhezi, quite endearing really. Quite active and quite unusual coloring/pattern, body shape and look)
P. senegalus (personally i would not go for it, too bland color imo)
P. oranatpinnis (asuming this is ornate bichir - then go for it)
Osteoglossum bicirrhosum (i got this one, if you never kept this one - i strongly suggest. It swims at the right speed: not too fast not too slow = elegant... unusual look also ...serpentine)
Scleropages jardini (i have this one, if you never had it - get it. torpedo look. Quite active swimer. Nice scale patterning = it is called pearl for a good reason. Next best thing if you want an an asian aro but can not get due to legal reasons)
In summary, i suggest a bare tank with bichir or motoro with any aro (or armatus though i am not sure how agro is this fish ... it certainly looks agro). If you are not constrained by legalities, go gold/red or rtg: scleropages formosus!!!!!
If you insist to have snakehead then you will need to decorate the tank a bit.
Completely non-predatorial fish: koi.... if you can afford, koi can really have nice and unusual patterns and colors (asagi, tancho to name a few)
PS: odd ball you like? Go, Bagarius Yarelli (same same snakehead set-up cause apparently quite shy and difficult to keep): very mean and toothy looking cat this one