If you are going for max profit and experience, you should try to smelt the highest tier bar for your level. For this article, we will assume that you are level 85 or higher, and can smelt all the bars needed. So bars such as adamantite or runite allow you to make much higher profits than making iron or steel bars. It might be more expensive to get all the raw materials needed to craft all of these high-level bars, but the profit will be well worth the cost of expenses. Gold bars are also some of the highest valued options in the world, so smithing some of those with the goldsmithing gauntlets will have you making a ton of coins in profit. If you can, go for the gold bars and start selling them!