I'd concur with Phil. I've tried the White Tower brand used by the majority of BIRs, and all the various supermarket and big name brands (Napolina, etc), and haven't been able to discern much difference in the finished curry.
That said, I do like my curries hot, so perhaps the chilli levels interfere with the detection of such subtleties. ;D
I'm currently using Tesco double concentrated puree, which does the job well enough, but as with all such matters, the best thing to do is try a few different brands and see which works for you...