I'm the same, Caltex being my preferred fuel. Several reasons:
1) Shell tend to price their fuel higher. My local shell won't display the price of diesel and when you get to the pump after waiting ages in line, it's already 4c a litre dearer than Caltex's price. BP comes in 2c/litre dearer than Caltex.
2) If I use a Woolworths voucher at Caltex, I'm saving 8c per litre compared to Shell, and 6c/litre compared to BP.
3) Caltex use "up to 2% biodiesel" in their diesel. In all that research about using 2-stroke fuels, I noticed that the best thing to put in your fuel to help reduce problems with the DPF was 5% biodiesel. Okay, 2% isn't 5%, but it's closer than 0%. Gimme.
I won't stop anywhere that doesn't have a decent turnover of diesel. The Caltex I use always sees small trucks and 4WDs at those bowsers. Don't see a lot at the Shell or the BP. When we're on the road, we look for servos that have good open entries and easy turning access to the diesel pumps - not only because we are pulling 7.5m of van behind us, but because if they are built like that, it's to let the trucks in and out - and they'd only go to that trouble if there was a need to do so.