Other than NO sweetener --rank the following based on how it will raise (or not raise) Blood sugar 1- being the best:
Stevia Organic Brown Rice Syrup RAW Honey Coconut Crystal/Syrup Yacon Lo Han
I prefer raw honey as it contains natural antibiotics, but I think self-experimentation might be the best option for you in terms of ranking which affects your personal blood sugar most directly.
I'm not qualified to rank all of those sweeteners, but I would recommend you look at more than just blood sugar when choosing a sweetener. For example, foods with a ton of fructose (like honey and agave nectar) score well on the glycemic index, but are more likely to make you fat than an artificial carb like dextrose.
That said, stevia causes the smallest effect on blood sugar out of those choices. Its GI score is 0. In fact, there may even be evidence that it lowers blood sugar levels.
Stevia won't likely at all but I tend to avoid it. (mutagenicity)
I like rice syrup simply because it's mostly glucose. You can manage how it affects your blood glucose by being active, maintaining excellent insulin sensitivity and the amount of fat with which you eat it.
It really doesn't affect me at all - but I'm eating very little of it usually in the form of ice cream or something like creme brulee....both of which are almost all fat.
Personally, I do like xylitol but most don't share my view. :D
"I'm kind of surprised that paleos would be recommending sweeteners that Grok would never, ever have had access to"
Again, some people view "paleo" as a useful template or paradigm, others as dogma.
I personally use http://en.wikipedia.org/wiki/Saccharin from time to time, usually in iced coffee.
Stevia or Xylitol.
However, Stevia has that.... weird chemical taste you need to get used to (acquired taste)
Xylitol is claimed to be good for teeth, the very reason it is in bunch of dental products.
General rule of thumb is to opt for natural over anything made in a lab, but depending on many factors, something like agave is not as great as some might believe. Here is a great post from Balanced Bites on sugars and sweeteners.
I'm kind of surprised that paleos would be recommending sweeteners that Grok would never, ever have had access to so theoretically we would not be best adapted to eat. Honey in very small quantities would seem to be the answer IMHO. There's nothing else that anyone has listed that comes directly out of nature.