My favourite pet of all time was my dog, named Babe -- part German Shepherd, part Gold Lab, and part Whippet (you can picture it -- a small lab with a brindled shoulder and deep chest/narrow waist -- and energy coming out of nowhere). But I've also had many cats.
I voted for cats for only one reason -- I'm 75 now, and don't walk as easily as I used to. Living with an active dog takes a huge amount of dedication to getting her out, exercised, socialized with other dogs and people. All of it is wonderful, but I no longer have the energy.
Cats can be very good companions -- so long as you don't mind getting your own way very often. (But that's the case with lovers and spouses, too, so no biggie.
) My last cat, who sadly had to be put down at 17 because of heart failure, was a wonderful companion to me -- less so to my partner. Though, I confess, when he was sleeping, she often didn't mind lying beside him and dropping her tail into his snoring mouth.