Haha, not an expert at all, I've only owned 370z a few months but I've looked into the exhaust setups.
For Op, it all depends on 1: your budget, and 2: do you intend to get a decat or high flow cat for maximum gains? Or are you only looking for a cat back exhaust.
I'd say the motordyne shockwave is perfectly balanced if you're going to keep the stock cats, although it's over £1900. However, if you then go and get a HFC or decat it then becomes one of the loudest setups possible. There are many cheaper options that will increase the volume.
If you choose one of the quieter cat backs you may find that this alone is not significantly louder, likewise a HFC or decat with the stock cat back won't drastically change the sound - but will noticeably improve it. all of the aftermarket cat backs are going to be noticeably louder than the stock system, whether that's enough for you I don't know. so it depends how loud you want. I suggest you search YouTube for "370z catback", find one or a combo you like and aim to replicate it. You can tell which cat backs are loud just by looking at them.
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I had Stillen cat backhand berk decats on my last 370z, just wondered about the Nismo set up difference