If you haven't access to a good sandblaster then paint stripper is your best choice. Wear eye protection ! Cheap rubber gloves too. I like the "gel" consistency better than the real thick goopy stuff. There'll be more elbow grease involved than blasting, may take multiple applications. Will also be some sanding, wire brushing and scraping with putty knife/screw driver to get into the tight spots. No matter what finish you apply afterwards thoroughly wash your parts with soap and water before applying the new finish. Baking soda and water rinse helps neutralize the acidic chemicals left behind by the stripper. Be careful to protect your eyes and skin ! Sandblasting is the easier choice, especially if you take it in someplace and pay. Perspective, you'll spend $10-20 on stripper for a whole bike, that much again on safety glasses, gloves, cheap paint brushes, and other cleaning supplies. You're gonna spend half a day on just the frame. If your local body shop, engine rebuilding shop, sandblasting service charges $50 or less for just the frame that's not unreasonable. Powder coat in certain instances can be a total bear to blast off. Two coat metallic (base/clear) especially. Hope this helps you out.