Generally speaking, opposite-sex pairs are the least troublesome combination. That does depend in large part on the individual dogs, though - I've had male-male fights, female-female fights, and male-female fights. In my experience, males fight more readily and often, but females fight more seriously and hold grudges. Spay/neuter does decrease the likelihood of conflict, as does a clear human leadership role (many fights are for 'pack position' - and actually most dogs do not want to be pack leaders, but rather feel as if they must; if the human is the clear leader, there's no need for the dogs to fill that position). I do recommend Patricia McConnell and Karen London's book, "Feeling Outnumbered", for multiple-dog households; it has very good practical suggestions for establishing leadership and setting guidelines for polite behavior. (Can be found at
www.dogwise.com and other online booksellers.)
As to personality - I find males to be more mellow and snuggly in general than females. (Not that my girls aren't snuggly and lovable, but it's different than the sweet, 'momma's boy' thing you get in a male.) Of course, again, the individual dog is the deciding factor and there will be some females who are complete snugglers and some males who are more independent.
