Cool Hand Lurker, The shop I grew up working in had a body shop as well. After a series of mysterious fish eyes ALL silicon based sprays were banned in the shop!
As for the OPs question. I have used many different sprays with varying effects. It seems to all come down to cost, supply, and preference. I personally feel like PB Blaster is better than the WD-40 penetrant and I think the 50/50 acetone ATF mix is better than the PB Blaster. Never have used Kroil, mostly because I never seem to find it on the shelf at my local suppliers, but everyone seems to rave about it.
On a similar but different note... Ive found that Original WD-40 works fantastic at taking sticky stuff off of surfaces, Like tape residue off of paint or glass. It doesn't hurt anything and cuts through the goo. Clean up can be a pain afterwards tho...
No matter what anyone thinks or says of the stuff I hope the OP has good luck with whatever rusty bits they will encounter!