Check out this link to H.I.T.H. information. Click on the photos as they open up large and clear!

www.fishdeals.com/fish_diseases/hole_in_head/

I FOUND THIS STATEMENT TO BE RATHER INTERESTING:
"Hole in the Head often occurs in aquariums with under gravel filters, and sometimes in aquariums with canister filters, but rarely in aquariums with a BIO-Wheel filters."

Yes, I have heard statement before. It's funny how they don't actually tell you why. I wonder if they actually know?

Under gravel filters aren't recommended because they become clogged up quite easily. Because Oscars are very messy, the risk is higher. A clogged filter means poor water quality. Poor water quality can contribute to hole in the head disease.
The only reason I can think of them mentioning canister filters does if you don't clean them out properly, they become clogged up with crap and can start producing lots of nitrate which again contributes to poor water conditions.

Personally, I don't think that any of these filters are as good as the canister filled so. The reason being is they just don't hold enough biological media. Take canister, you can get absolutely loads in them. You need lots of biological media to deal with the waste. Most of these Hob filters aren't very big and they only hold spongers far as I know. In my opinion, spongers not as efficient as bio balls and similar type media.

Oscars are incredibly messy, you really need a really good filter to deal with all that and I would always recommend a large canister filter, or a large sump filter. This is what I will be having on my new tank, 85 gallon sump filter. Imagine how much filtration you can pack into that?

I agree and you are probably correct about clogging etc. leading to poor water conditions. I also agree canisters "can" hold a good deal of bio material and work really well if cleaned properly and not "over cleaned". I like bio-wheels and the tank my two Oscars are in right now only has one large bio wheel that I know is being over taxed. The new aquarium (that hasn't finished cycling yet) has four of those same large bio wheels so the bio filtration will be pretty darned good. Yet I may add a canister to supplement the filtration anyway. I'm just really starting to get ammonia readings in the new tank and see no signs even of nitrites just yet so it will take another few weeks I feel before the tank will be ready.
I've got a small school of zebra danios (about a dozen) in there to help it get going plus 3 cory catfish too.

Many people I feel tend to overclean their filters, especially canisters. Bio wheels are pretty straight forward and there are warnings start to finish from the filter manufacturer that you leave it alone, dont clean it and just let it be unless it stops moving.
The aquarium "cycle" is probably the hardest thing for aquarists to actually learn and even after established can be easily upset by overloading with fish, over-cleaning or washing off the biological part of the filter. I have read several times that even established cycled aquariums don't really get "good" and fully established biologically for close to a full year.

Then so many people we hear from buy an aquarium on a saturday, fill it with water on saturday night and buy a stock of fish for it on sunday. It's lie you said Penn, the pet stores don't dare tell people what is really involved less they lose alot of customers because of the work involved and the time necessary.