I was in the same situation last year- I had a very active boy and got a very active and a little younger kitty girl to go with it. Kiri the girl grew fast into a kind of bully and is the dominating kitty here. Little Orion is more quiet now and plays actively only when she is not around.
The generation before was 2 active boys and I feel I would rather go with another boy if I had to take the decision again. But of course we love them both very much and wouldn't trade them