Well, it started with a black and stainless Seiko 7T32 which I bought when I was 21. I wore it nearly every day for around 20 years so in many ways that is my 'longest' favourite. I continued adding more Seiko 7T32 and 7T42 to my collection until about 2 years ago when I really got into reps.
I've always loved Omega Seamasters so it was a natural progression to buy some. I bought a new gen blue Seamaster chrono 18 months ago but decided that it was almost too nice to wear so I started hunting for a black rep of the same. I eventually found one and that was my first chrono rep. I then needed a blue one and now have 2 pre 2008 and 2 post 2008 Seamaster chronos. However two of them need some work and will be frankened - both need new crowns/tubes and one will have a gen white dial installed (once it's been relumed), the other already has an orange PO insert fitted.
So, I guess the simple answer to my favourite chrono question is one of my Seamaster chronos. (Currently my gen titanium on an olive green strap).
I really should have more 'love' for my gen Speedy Pro but she is mostly a box queen.
One thing I've learned over the past couple of years is that I'm generally better off buying either a used gen or a new/used rep as I don't like getting desk diving marks on $4k gens!