I'm hungry enough to say that I'd like to see Carly, too. Please don't hurt the tomatoes and eggs as you throw them at me.
Carly was always a favourite of mine, and she got terrible story the last time around. If I couldn't have Isabella, I'd pick her. It would also depend on - are we talking about a SHORT visit - or a RETURN. And is it going to be a "hey, hi, how are ya" thing or a story point?
I think April Ramirez coming to town for a few weeks could really shake things up with JJ/Paige. April and Mike had this "great thing" once upon a time, but I'd bet $20 that JJ's never heard her name mentioned. That could get him to thinking - he's young, and if it doesn't work with Paige...it's NOT the end of the world.
That being said, I REALLY HOPE we're not still dealing with Paige/JJ by the time the 50th rolls around. Or summer!!