Chain and sprocket

[Simon.Pieman]

You will always get a million different answers to this question.
Fwiw the fact is that like tyres and brake pads you should always buy the best you can afford.
TBH most people should never have to replace a c&s set these days.
I personally buy individual parts a they can often be got cheaper that way. Search eBay for the size and length of chain you want rather than for your bike and also cross reference your sprockets with other bikes too, my fazer 8 used the fitment rear  sprocket and exactly the same front sprocket as my tdm (same brake pads too)
As for what brand you should buy, well, to some extent it depends on your use of the bike.
If you're a weekend warrior then an o ring chain and JT sprockets will be fine but I'd you do more regular riding them an x-ring chain with afam sprockets.
If you are a high mileage rider like me (25000 miles/year) I would suggest DID X-RING chain and renthal sprockets.
I get around 35000 miles from a set with a scottoiler.
Ultimately though I guess money is king here as none of them are cheap.

You neglected to mention that the chain needs to be ZVM rated, all chains of this type (new stock) are X ring anyway and usually north of £150 to buy. Anything that costs less than that is probably not ZVM.
I fit the above with Renthal sprocket at the rear and Yamaha standard front sprocket (quieter than a Renthal front sprocket). Chain and rear sprocket lasts me about 35 to 40,000 miles when I usually find some links starting to gaul up, I change the front for a new at 15,000 (visible wear by then). I use old engine oil for lube -very sparingly, maybe a teaspoon full applied with a small paintbrush every hundred miles or so.