Truvia is derived from the stevia plant, which is naturally sweet, and erythritol, a sugar alcohol, which can be found in melons and grapes. Splenda goes through a chemical process to make it into sucralose. Natural ingredients are typically safer.
To make Truvia, the stevia leaves are brewed like a tea and it is then concentrated. Once concentrated, it gets combined with erythritol to provide it some bulk to make it look more like sugar. Since it is derived from natural ingredients and contains no sugar, it has no effect on glycemic index, making it ideal for those with Type 2 Diabetes.
Splenda is made from sugar. It goes through a complex process where the sucralose is extracted and then blended with corn-based ingredients to make it the right level of sweetness that is comparable to regular sugar. While long-range studies have not been widely done, the belief is that because of its chemical process, it is comparable to aspartame. Aspartame can enter the blood brain barrier and wreak havoc on the brain center because it is an unnatural chemical compound, like Splenda.
Truvia is derived from a plant that is found sweet in nature and requires a simple brewing process to extract the sweetness without any harsh chemicals being used, making it generally safe for the consumer to use.