One AC500 vs Two AC300...

[yhbae]

So which is better - single AquaClear 500 or two Aqua Clear 300?

From flow rate perspective, 2xAC300 wins. It wins from redundancy perspective as well. So what is the disadvantage other than the cost? (2xAC300 is more expensive than AC500)...

I'm curious to hear other people's opinion on this as well...

By the way, this is going to be a filter setup for a 36x18 tank, heavily stocked with mbuna.

 

[jjsdad]

IMHO there aren't any disadvantages.
As you say the redundancy is great and the extra filtering can't be beat.
Place them as far apart as you can and Bob's your uncle.