I suppose take my opinions with a grain of salt, since I'm 21 and my three dolls (Samantha, Kirsten, Josephina) came from when AG was owned by Pleasant Company, and infinitely better than what Mattel has done to the line.
I personally think the historical characters are best. I feel like a "look like me" doll with modern accessories isn't anything special, but the historical girls came with stories which were very appropriate for the age group. Each girl had 6 books and they deal with issues like women's rights, racism, patriotism, what it means to be an American, growing up, what it means to be a good friend, tolerance, etc. in a very good way. They also had historical info in the back, and that can help springboard more research and a lot of interest in history for your daughter. I believe now there are also short stories and such for each doll.
If it were me, I would pick a time period your daughter has a lot of interest in, and do the doll and book set for that. I know some of the girls are being retired. Samantha, my first and favorite was taken away last year I think. And I believe Felicity may be next. Which is crap cause those two girls were both fantastic. I don't know much about the newer girls, but Molly is always fun.
I dunno, call me old fashioned but I liked the girls with full-fledged personalities girls could actually relate to over just another dress-up doll. The products are still good, don't get me wrong, but I think all of this "Girl of Today" stuff with all these limited edition things to get people to buy a doll every year is crap. I ended up being spoiled by relatives hence I had three, but frankly you used to be able to get one doll and never run out of clothes, accessories, short stories... I even had the cookbooks. And why make movies about girls they later discontinued?
Edited to add: The dolls have fabric bodies and their heads rotate, as well as their legs and arms where they attach to the bodies. Their eyes close if you lay them down. I found them to hold up very well. Just make sure your DD knows its a special doll that shouldn't be tossed around, stepped on, gotten in the mud...whatever.

18" dolls are common, so if you sew or know a sewer, its possible to make/buy doll patterns and not bother with buying AG's outfits unless you want a specific outfit you can't recreate.