Well, I have two female minpins and they get along fabulously but I USED to have two female minpins who did NOT get along - and all were fixed - so it really does seem to be personality. If they are BOTH very dominant, it can be trouble but I've much more often heard about it with two FEMALES than with two males.
The main reason I have female minpins is they use a litter box inside and a male lifting its leg to pee INSIDE the house is uhm... a HUGE PITA!! Been there, done that, never again!
I do find males are more affectionate and cuddly and almost more "needy" but also quicker to bounce back and super happy little fellas but I've only HAD male shelties so I honestly couldn't say.
I know in minpins, the male we had at one time was MUCH less dominant than the females and MUCH clingier and sweet than the females (not to say the females aren't sweet but you guys know what I mean!!!)
It's kind of the difference between men and women. Put 10 men in a room and they can often get along talking about sports or something.
Put 10 women in a room and if a few are VERY different from the other on things like child rearing or whatever, it can get nasty kind of quickly!

Have fun!!!