I thought Ally will be happier in her own house, with her own food, toys etc, but I'd appreciate your opinions.
I think you already have your answer. Unless your cat is especially adventurous and loves new things, I think he/she would be best left at home with the familiar surroundings. Mimi was boarded many times when she was younger. She had a huge cage to play in, in the hands of people I trusted, but this has been many years ago. Since that time, I have always had someone (either a friend, or more recently, a trusted petsitter) to care for her and the others when I am away.

My opinion, obviously.