Here's an atticle with a comparison of the Sunfire with Velo and Pinnacle. I have a Sunfire TrueSub II and have been very pleased with it for home theater (considering the size; and for a smaller room). You aren't going to get the value, as far as price/performance, with a smaller sub that you get with the larger subs, though.
The earthquake MKIV12 is new so I haven't had a chance to hear one. I have a MKIV10 demo unit that I am really impressed with, I personaly think that it has about the same output and quality as the sunfire. I use the MKV15 supernova in my theater room and it is an awsome sub, however it is a quite a bit more than the MKI's. The MKI's are a really good value.
If you are only looking at those three, then the answer is really easy - the Earthquake. It has as much output as many 15" and some 18" subs (see the older tests/reviews on their site.) You can get the MkIV version relatively cheap now that the MkV are out.
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