Blasting make the most sense.
There's been a lot of debate on which type of media is best - sand, walnut shells, soda, plastic, etc.
I've had it done a number of ways and in my opinion plain blasting sand works best because it removes 'everything' and leaves you with the least amount of prep work. It also leaves you with the best anchor profile for your primer to adhere to.
The plastics/baking soda will leave the metal too smooth and won't remove rust. But if you have a fiberglass piece they work well.
The hard part is to find someone you can trust to do the job quickly and properly. We've all heard stories of guys who take 6 months to get the job done, and guys who over pressure the sand and damage the panels.