I just went through this debate and spoke with many autobody guys. Some have a preference for this or that. I started off thinking of getting it chemically dipped. It was going to caost me around $2400 for the entire 1/2 ton truck body parts. I was steered clear of this method due to the "leaking from seams and ruining paint" problem. I was then looking at getting it soda blasted. The problem with using soda is that you need to neutralize the metal before priming and if you do not do it properly, the primer will not stick to the metal. My bodyman told me he had lots of problems with this. He also said that they recommend washing it off with water and we all know that bare metal and water don't mix too well. Soda blasting was going to cost me $1400.
I ended up going with walnut shell blasting. It is gentle on body panels, does not heat up like sand and warp panels and the metal does not have any residue afterwards. You just need to wipe down the metal and prime it. It worked out fabulously and I was very impressed at how clean it got the metal...even in the areas that had a ton of bondo caked on. Walnut blasting ended up costing me $900. So in the end I saved a boatload of money (first time for everything in this project I guess!) and it worked out great. I highly recommend it!
