I think BrightSpark is basically correct in that most people would prefer to see a main dealer stamp in a service book than that of a non-authorised dealer. Having said that, there are good dealers and bad dealers in both camps.
Let me give you examples. Many years ago, when I used to do most of my own servicing/repairs, I took my still-under-warranty car to a very small Vauxhall main dealer for a service (when you HAD to use a dealer). When I collected it they daid they'd had to replace the front disc pads because of wear. I'd checked the pads myself not long before the service and didn't think they needed replacement. When I asked to see the old pads they'd been "thrown away". I had little choice but to pay.
Some years later, when I'd replaced the Vauxhall with a Volvo, I took the car in for service. I got a phone call saying the front pads needed replacing, so I said that that was a job I did myself. "They really do need replacing urgently"; "It's OK, I like to do it myself", "we'll do the job for just the cost of the pads since we're doing the service"; "No, it's OK, I like to do it". I got the car back and, since I actually had the pads, I thought I'd better get them changed sooner rather than later. I stripped the brakes down and found new pads had been fitted, no charge. That's what I call an honest garage and I still use them 15 years on.