Define "monster".
Big fish have a presence and a charm that little dinks like tetras and guppies just can't match...but the appeal ceases to exist when they are shoehorned into undersized housing that stunts their physical and behavioural development...and this happens a lot. The puppy-dog-like responsiveness of a large Oscar in a 75 gallon, or the endless circling of a big Arowana or Gar in a 200 gallon, have a certain sad, pathetic quality to them. Nowhere to go...nothin' to do...
So...if one truly has the facilities to maintain monsters...and doesn't amass them in quantities, jamming them into tiny tanks which they optimistically label "grow-outs" while day-dreaming about larger tanks they don't have yet...then, yes, monster fish are unbeatable.
For most of we mere mortals, small- to mid-size fish offer a much better chance to provide healthy, humane housing that allows us to observe natural behaviour. Chihuahuas aren't Great Danes, but they're still dogs and they're still great.
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