I'm 6' tall. Barefoot. haha...although I have very little dance experience at this point, based on what I've experienced in my ballroom class last quarter, there's no set ideal...and I'm glad too, cause, needless to say, it's tough to find a partner taller than me - especially if I put heels on, haha. During my ballroom class I danced with a wide variety guys anywhere from waaaay shorter than me to significantly taller than me; when I think about which ones were easiest to dance with, four actually come to mind...one was about six inches taller than me, a big football player; one was just a couple inches taller than me; one is two inches shorter than me; and one is waaaaaay shorter than me.
Sometimes there are some adaptations that need to be made to make it work with shorter partners, depending on what we're doing. In particular, I find that some dips tend to be difficult to execute when I'm with a much shorter partner. Or, for example, the guy who is just two inches shorter than me is teaching me lifts, and height definitely effects some of them...but if we just keep that in mind and adjust accordingly, it works out. He was originally afraid to do some of the lifts with me and made me practice them with taller partners for fear that my height would get someone hurt, but we've started figuring out how to do all of them despite our height differences.
Overall I guess I've found that it's just a matter of personal preference and adaptation...different heights work for different people...which seems to be the general consensus of this thread!