Obviously it will depend on the cat, but here are my two cents. We have three kittens - two of which are male. We got them fixed about two weeks ago (they are about 7 months old) and have had no problems with them at all. They never sprayed or anything, so that has not been a concern, but they are so much more chilled out and relaxed than our girl kitten (who was altered about two months ago).
My husband has had cats his entire life and he has always said his girl cats are a bit more standoffish - lovely and wonderful, but very much about things on their own terms. His boys, on the other hand, have always been these relaxed, chilled out lover-boys. I have noticed this with our boy Paddington since getting him fixed. He is by far the most affectionate of our cats (and considering these are former feral kittens, it is AMAZING). Again, it varies from cat to cat, but based on my anecdotal research (friends, husband) fixed boys (on the whole - there are always exceptions!) make great, lovable companions. (But my girl kitten is awesome as well!)