Mauricio
You can do either really. A common setup is to
1) make core switch 1 STP root for all odd vlans and match this up with the HSRP active for the odd vlans.
2) make core switch 2 STP root for all even vlans and match this up with the HSRP active for the even vlans.
Core switch 1 will be STP secondary for even vlans and core switch 2 will be STP secondary for odd vlans.
This setup works fine and utilises both the uplinks from the floor switches.
I'm assuming that the etherchannel between the core switches is a L2 etherchannel trunk ?
Jon
