When I were getting labs to do colour I used peak imaging and the darkroom interchangeably, smaller batches work out cheaper at the darkroom, larger batches at peak.
Both have excellent standards, but peak normally takes a day longer than the darkroom to return (Their freepost service to get the film to them is 2nd class, where as the darkroom is 1st class)

That said, I've not looked back since I picked up a Jobo unit and started to do the job myself