Pros and cons:
The BioWheel mixes air and water, not to mention the large amount of surface area afforded by the accordion-shaped media, making for excellent bio-filtration. Probably the best out of the
HOB filters. The only ones that would have better bio-filtration, while the BioWheel is working properly, would be fluidized sand bed or larger wet/dry filters.
Unfortunately, the BioWheel has a habit of slowing down or even stopping as it gets loaded up, causing it to lose its excellent bio-filtration.
The Aquaclear (and other, similar HOBs like the Whisper) are extremely dependable.
Both types of filter have filter cartridges you can load with whatever media you want. I've got my Marineland loaded with ceramic planting media, so even if the drums stop spinning, I'll still be getting a ton of biological filtration.