Hi
I can only speak of the print reseller schemes i've used but RCS come out tops. Their bolt-on prices are quite high, but this can be made back easily when you take advantage of their 2 free deliveries per week (for the top bolt on). Also they have started to offer a free upgrade per month, halving their standard production times - invaluable when you get a last minute job from a client, you can mark up loads as the clients is desperate to get their stuff.
With RCS you know where you stand, they say its getting despatched on Thursday? You know 150% that it will, peace of mind helps when running a business. Guaranteed despatch times are a life saver for a business built around customer service. You get what you pay for in this world.
Another one worth looking at is
www.multicolourprint.info - dont do a huge range but pretty keen on business cards and absolutely top notch quality.
Sense Creative however is worth avoiding AT ALL COSTS - absolute sharks of the print world. Run by John Thompson, the rudest man in business by far!! As has been discussed, if you get a problem - AND YOU WILL if you're doing volumes with them then forget any satisfactory resolution with them and be prepared to be spoken to like a piece of dirt by John. Shame as their prices are the best in the industry, but service and turnaround times are like a lottery!!
RCS is worth a shot if you're serious. My experience of local printers are small margins as they tend to be quite expensive as they don't do the volumes of the likes of RCS and other online print companies. Its still possible to build a relationship online, everyone is based somewhere and can be visited if you need to build a special relationship.