Personally I always encourage two. If you watched them interact with each other you would understand why! They love the company of their own kind and we are a poor substitute for that! However I do understand that in not all cases this is required or possible and so I am happy to sell independent budgies.

Are males or females more friendly?

I have had a lot of experience with both- I believe each budgie is individual. Overall people do say males tend to be friendlier and easier to tame, however the ones I have ended up with close relationships with have all been nosey little females!
If you watch the budgies, after a few mins you can see their personalities shining through... budgies that are at the front being nosey watching you will tend to be quicker to tame, regardless of gender.
I have never personally taught a budgie to talk, but have been told that males tend to be the ones that's end to talk as in the wild, they would be the ones to call the females.