Think its going to be a matter of checking them all out James, as I wouldn't recomment Arnold Clark at all. Everyone is different as you can see by the replies ^^^
Verve at Crow Road is where I got my turbo, and I've had no bother at all from them. I've had a couple of minor common faults on my car, and when I've phoned, car has been down next day and fixed straight away, servicing not had any problems with either. I know a few guys that work in Verve Service Department, so mibbie that helps, but I know my car is looked after. I've also had a few things under warranty and they've never hit out with, sorry can't as you've modded your car, your warranty is void. Suppose it all just depends.
There are however a few salesmen I would steer clear of, you can spot them a mile away, but surprisingly there are a few good guys in there.