Prilosec is considered more effective both from what I've read and experienced. I recall a Wall Street Journal story about how the owner of both the Prilosec and Nexium drugs had developed Nexium to prepare for Prilosec's patent expiraton. The company was spending millions advertising Nexium to doctors and patients to get them to switch even though Nexium never out-performed Prilosec.

I also wouldn't think of them as 'Heavy Duty Antacids'. Prilosec takes some time to work (at least a few hours). There are some variations of, IIRC, Zantac that are combined with traditional antacids that are better for immediate relief.