Splenda is Sucralose, and is known by many other generic names depending on your store. It's all the same Sucralose. Walden Farms uses Sucralose. Stevia is in many different forms and packages - Sweet Leaf I believe is the 'most pure form' that has no fillers, etc. added to it, so for straight purity sake, that is probably the best brand choice of all the sweeteners. Steer clear of aspartame.
My coach advised me to keep those extras at 6 or less per day, they still have hidden calories and carbs - e.g., 1 packet of Splenda has ~4 calories and 0.9g carbs - just enough to squeak by the FDA labeling guidelines of 'zero'. Make sure to always write down all the extras, even if they are '0/0/0' - some folks have found they have a sensitivity to certain items, so it's just a good idea to keep track.
As for the Truvia question - it's been addressed before:
I saw someone post that we shouldnt use Truvia as a sweetener. According to my coaches and many other resources, thats not true. Here's the story and the science why its ok...(but still only use in moderation! I have never used more than 3 packets MAX per day, with 1 packet being average.)
When I looked on the Truvia box, it said that it contained 3 carbs. So why is that allowed? Here is the why...
One of the most frequently asked questions by carb conscious consumers is whether they should count the 3 grams of carbohydrate on the label. The answer is NO. Here's why…
http://www.3fatchicks.com/forum/4369722-post389.html