Aftertaste seems to be in the eye of the beholder. To me, aspartame and Splenda have very little aftertaste. The stevia sweeteners are more unpredictable (some have an aftertaste I don't like, and some are fine).
You might consider trying one of the sugar alcohols (like xylitol). I like xylitol (it does have a cooling sensation on the tongue which you may or may not like), however it may have nearly as many calories as sugar for some people (there's some evidence that some people may digest some sugar alcohols better than other people).
Erythritol is supposedly much lower in calorie, however it's also more likely to cause the digestive issues notorious of sugar alcohols (any and all of them can cause abdominal cramping, diarrhea, and foul gas).
For myself I actually am glad of this effect (no I don't like getting diarrhea and stinky gas), but I do like that the potential consequences assist me in portion control (one serving usually doesn't cause me any problems whatsoever, so the threat of ill-effects is an effective deterent to overindulging).
You also may find that a blend of sweeteners is sweeter and has less of an aftertaste than a single sweetener. For example, I don't detect an aftertaste when using Splenda in cold beverages or food, but find a very unpleasant aftertaste when used in blending. When I used a mix of xylitol and Splenda in a gluten-free banana bread I made recently, there was no aftertaste at all.
Also - when it comes to Splenda, sometimes it's not the sucralose (the sweetener) it's the bulking agent that people dislike. That means that you might find that some brands of sucralose (store brands, for example) may taste better to you, because they use a different bulking agent.
Or you could try undiluted sucralose, liquid sucralose, or Torani or Davinci sugar free syrups. I've only evern seen undiluted sucralose and liquid sucralose available online (such as on amazon.com). The problem with both for baking is that they are MUCH stronger than the powder, so they don't substitute for sugar in one-to-one proportions. This can change the consistency of baked goods - you may have to adjust the other ingredients to come out with a successful product.