I have 3 Cisco switches. Should I use standard switch ports or SFP ports for spanning tree? What are the benefits to using the SFP ports?
The first question has been answered, but I'd like to elaborate on the second.
What is the benefits of using SFP port?
There is no benefit to using an SFP port for spanning tree. Spanning tree protocol runs over ethernet there is no difference (to the switch) between the ethernet of the copper 1000base-T and fibre-optic 1000base-SX (or LX) connection.
Of course, if you're doing a run that's over 100m to the next switch you'll need to use the SFP slot and make the connection over fibre but spanning tree will act the same that way as it would if the next switch is connected with a 10m cat-5e cable.