Once they've been spayed/neutered, there is little difference. It's
possible males will roam a little further but it's not really a major
problem.

Don't forget to get them microchipped..!

Ivor

It depends on the nature of the furballs  some cats can never get along with
other cats.
As Ivor pointed out either or.  Just make sure they get neutered before they
go into heat

I don't think it makes a great deal of difference once they have been
spay/neutered.  Instead, I would recommend that you look for a pair (either
kittens or adults) that have *already* been paired with each other.  They
could be litter mates, or they could be cats that have lived in the same
home with each other.  That greatly diminishes the possibility of problems
when you introduce two cats into a home simultaneously.  Animal shelters and
rescue groups usually have a number of these "bonded pairs" available.

MaryL