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I think that intercoolers best benefits are in improving temperature management rather than delivering quantifiable bhp gains in the same way as an air intake can do for example.
So perhaps your question should be which intercooler is the most efficient and durable. I would avoid the fleeBay Chinese copies even if their prices are as cheap as chips. It's all about the detail build.
It would help if you said which car you want an intercooler for and what its existing mods are. You don't necessarily need one unless you do trackdays or are Stage 2+.