Bike fit / correct riding position

So I've booked in a session with the Bike Whisperer, but I'm really umming and ahhing about which bike to take.

Should I take

1. A bike that I'm probably going to replace with a new build in the
   next few months and use the numbers for the frame picking/setup?
   
2. A bike that I'm already pretty comfortable on and dial that fit in, and
   use the numbers for the new build?