I'd have to go with acrylic, my daughter and grandkids are allergic to wool and having something those I love are allergic to is a problem for me. However, if I could actually afford it and was willing to deal with the cleaning issue, I would do one in wool and figure those who would have a problem with it should avoid it. Ambivalent? LOL I think a wool afghan could be much more beautiful than one done in synthetics.
No way I'd knit it in wool. Can you imagine washing and laying it flat or whatever to dry?? I'd go with acrylic. I have a couple acrylic afghans and they are plenty warm in the house where we use them.
When asking questions ALWAYS post the name and a link for the pattern if you have it.
Wool afghan...dont think so as with children they spill things and some will even put it in the wash to hide what they did...do you want your work to be the size of a washcloth ??? cause they would run it thru the dryer...We could see the steam comming from your ears on that ....safer to make it oput of acrylic...I have tons of acrylic afghans and love all of them. Yep grandkids have spilt things on them lots...better safe and happy than the other....
Choose easy care - it's something of a myth that acrylic isn't as warm as wool, it can be, if not warmer. That only applies to outer wear that wet wool will be warmer than acrylic, but that wouldn't be of concern in an afghan.
Either acrylic or superwash worsted wool, whichever is more affordable.
That said, my MIL knitted the most gorgeous afghans using Red Heart Acrylic. For some reason hers always came out very soft. The ones I crocheted with RH never softened even after washing. YMMV, and please let us see your finished afghan, regardless of which yarn you choose to go with.