Will a bio-wheel work ok with a oscar, if not what should I get.

Yeah, a bio-wheel, as long as it is rated for your tank size, if not, you might have get two filters. Personally, I prefer canister filters, they make them in lots of different variety of sizes.

The only bad thing about BIO-wheels--you must NEVER let them dry out!!! Which can happen quickly. Bacteria die REAL FAST when they get dry. For bacteria, I like (1) Corner old fashioned filters. Just put a few sterile rocks in them to keep them on the bottom; the rest with filter floss and leave them alone. Powered with a simple air hose. Those things get really brown in a short time which means--bacteria. I have a liking for those filters too that you hang on the ouside of the tank. AQUA-TECH has awesome filters with a biological section that is never changed. It gets real brown and stays that way. The good thing about it--if you get a new tank, you can just tranfer them over to the new tank and get it cycling REAL fast, along with keeping the water 82 degrees.

I DO NOT USE CARBON IN MY TANKS. HOWEVER, with establishing a NEW tank, use them for a few months until you get a good supply of bacteria. Then discontinue all carbon. I will also use carbon only to remove chemicals deliberately. With lots of bacteria, you really DON'T need carbon--that and keeping the water swept of poo. And limiting fish. I mean one fish per 75 gallons makes it easier.

I had a canister filter and one day it started leaking and huge quanitites of water was on the floor. After that I have been afraid to use them. I know that's not normally the case, but that's what happened to me.

I've had both Cannisters (Large ones) and Bio Wheel canopy filters and I just purchased a large Bio Wheel canopy that has 4 big bio wheels in it. I like the convenience and the bio wheels keep the water oxygenated enough that you don't need noisy pesky air pumps and air stones. That Marineland Bio Wheel canopy they make up to 48" long and other then that you need to look at a bio wheel hang on filter. Personally if I had a Tank over 48" in length I would recommend at least one of each, cannister and bio wheel.