I agree with Troy (Roy). If you are confident in your mechanic's abilities, then it is better to get it all done at the same place. Service, tune, upgrades, rebuild, etc; if it's all done by the one w/shop, then they know what is done to the car, how you drive it, and how well you maintain it. If you keep switching w/shops, and something goes wrong, then they'll point the finger at the work done by the other shop.
I have stuck with EAS for 6yrs, my ecu choice was based on what EAS where comfortable tunning, all upgrades and fabrications were completed by EAS and i couldn't be happier with their quality of work. After 6yrs of subtle abuse on track days, cruises and Motokhanas and making double the factory power, my engine gave up after a track session at Calder Park. So now EAS are building me a new engine, that will handle the abuse. Over the 6yrs with EAS i have seen plenty of strong engines leave the w/shop.
Some people have different opinions on different w/shops, at the end of the day, you just got to filter out all the BS.
There is no doubt Racepace has the best reputation for RB engines, and rightfully so, but i personally believe there are other w/shops in VIC that can also build, strong reliable RB engines.
Also someone mentioned that some w/shops will not tell you all the details/secrets of the engine build; this is so true. Why should someone reveal all they secrets that make their engines strong and reliable. This is their living, their bread and butter, so they'll just tell you the basics.