Judy, I have used honey, agave, and xylitol all interchanged equally. Stevia and xylitol both can be contaminated with corn but neither have to be avoided as long as you can get them from a good source. Of course use way much less stevia than the others, I've never converted to stevia as I don't care for the taste of it if used alone. Xylitol and stevia have a zero glycemic index so they are better for those with candida issues. From what I understand is that some people have a gut reaction to xylitol due to it being an anti-candida, so you can get a die off reaction. I would say just start with a small amount and then gradually increase as tolerated. I'm not sure on your question about what it does to animals and how that compares to us, I would be curious to hear from anyone with knowledge on this.
Another option you may look into is coconut palm sugar. It is also lower on glycemic index (just not zero like xylitol and stevia) and interchanged equally with honey and agave. All these above mentioned sweetners are natural. I do not use cane sugar, although it is also natural and safe, it seems to bother me, maybe too high GI?
Hope this helps and hope your cold is gone! (I have one too right now)