Arowana of course..both become big...but RTC more....and it cloudes the water like crazy...
They spend most of their time in the bottom...
Arowana is much better..!!
I've never owned an RTC but the big ones I've seen in public displays just seem to sit there. IMO if you've got a tank big enough to house a RTC you could make it far more interesting and have more "personality" fish with an aro and some tankmates.