I have 05 Accord EX Coupe 4CYL

I talk to with people who work for exhaust, If I go with dual exhaust then I will loose torqe, and this guy said he only do custom exhaust, and he said if I do with single exhaust, I still will loose some power.

than, if I get any exhaust, I will loose some power?

And what would be the best exhaust do you guys recommend?
I am looking at Greddy....