Effective car paint removal is the basis for any good paint job. Paint removal sprays are great for removing overspray, but if you need to take it down to bare metal, orbital sanders are much more effective and efficient than any spray or gel paint removal products. The main reason for this is that paint removal gels and sprays must penetrate the paint completely to sufficiently loosen it to allow the paint to be scraped and removed. With a 100 grit pad on an orbital sander, paint removal will go much faster and be much more complete.
For more info, see Five Things to Know About Car Bodywork Repair