The Peng filter's Bio Wheel ripples the water more, while the ACs just let it fall into the tank. If your water line is high enough there will be little movement with the ACs, and more with the Peng.
There are two things they need to improve on the AC.
1. Raise the outside edge by 5mm. If you put in near capacity filter media, AC always looks to be on the verge of spilling. Personally it hasn't happened to me but I have seen thread here about AC spilling over the top.
2. The motor frequently fails to start after maintenance outage. It is not a big deal now that I have discovered I can kick start it with a toothpick without detaching the motor assembly. (The one Whisper I have NEVER stalls.)
I have never had problem with my Bio-wheel 330. It is very quite. I do agree that the current is very strong and there is no flow control. I guess they want to keep the wheel spinning. I can understand why my pearl gouramis don't like to go near that part of the tank. I am considering modding the cover with something to extend down to the water surface to block the current. Any other ideas?
I think you guys are using "current" and "surface disruption" interchangeably.
A Penguin 330 has a rated flowrate of 330 GPH, which it distributes out of two chutes with a combined width of about 10-11 inches. An AC 300 has a rated flowrate of 300 GPH which it distributes out of a chute about 7 inches wide. Which creates more current?
I would sum it up like this... both are great choices. Aquaclears are the longest lasting, most versatility in media, are the most quiet, create a good current and disturb the surface less. Its all about if you prefer a biowheel. Biowheel's are the next best thing to a canister filter for the promotion of bacteria. But they suck on a planted tank, just as wet/dry filters do, which it really is in a way. They are noisier.
I have a rena xp2 canister filter for sale. lol if you give up on the hang on back concept. Canisters are the best.