I have used both Emerald (twice with my old Superlight when Dave was able to get the most hp possible after DVA attention to cams, verniers, porting and induction) and Track & Road once (when Steve mapped my current CSR260) - which totally transformed its 'drivability'.
IMHO both are extremely good and I would happily use the services of either again - it probably does come down to distance and available booking slots.
Paul
CSR Superlight 260 Mclaren Orange
Power by COSWORTH Pictures here