most effective bass traps

It seems that ASC has very popular bass traps, but at a significant cost. There are other companies that claim to have more effective bass traps. Is there any empirical (or subjective) evidence that one companies traps are more effective than another?
Anyone tried the bass traps from the company the 'foam factory'? They seem cheaper than the others and there is also free shipping on orders over $75.
The ones in the corners.

Depends on the frequencies you want to trap. Although I'm skeptical of their product claims to go as deep as they state, I'm in no position to argue. The methods of measuring sabines for an individual trap have little to do with a typical listening position or overall effectiveness. It might be fun to have a shootout between the brands with a single microphone in the same room. Should the constraints be dollars or square footage? Would it be relevant? Probably not. It wouldn't be your room and your speakers.

The science of these is not complex, often misunderstood and, sometimes, misrepresented. What it comes down to is addressing your unique situation, which is the probably the least understood. However, no matter which brand or type, most who have just taken a stab at it have been impressed with almost everything, which seems to indicate it's all worthwhile.
Read everything you can on the website. They give you the best information with wonderfully comprehensive details.

FYI: Foam is not all that effective as a bass trap even if the website selling it says so. Compressed fiberglass or bonded acoustical cotton are leagues better down load and across the board.
Do a search here for "superchunks" find all sorts of links. One of them has test results plotted. SC's will match or beat nearly anything out there for a whole lot less$$...and they can look nice, or invisible if you finish off the corners of the walls.
Thanks for all the responses thus far. I have seen the data on the Real Traps and other websites. It's difficult for me to view the data as objective since I have no direct knowlege of the subject and the results support the product being advertised. Asthetics is important. Interestingly, I just had my room professionally acoustically treated. The focus was on the upper frequencies. The reason for asking this question is just in case this treatment leaves any low frequency issues unresolved.