As Joe said: try them all... it's different all the time, even with the same driver details, between companies... and wildly different between drivers even if they have similar ncb and age.
In your case, as it is a bit more "bespoke" (X years ncb on commercial vehicles and Y years as a named driver), it really will take a bit of leg work - and could pay real dividends going through the effort. Other than the usual big companies... a lot of the time you need to find a good broker who will go to bat for you (sometimes with even the same big companies and often get you a better deal and direct). Brokers also have a certain amount of flexibility when it comes to they are willing to accept (like perhaps part of your commercial ncb). As a rule btw, all named driving ncb time counts at 50%.
Ps over the years I've had the STI insured direct with AXA, indirect with AXA via AA, and the past years I've had trade insurance so no longer need to worry about individual cars as it is just a flat fee. One thing to also ask for is if a fleet policy might yield you a reasonable deal (the 2 commercials and the STI). Good luck.