SFP 1000Mbps vs 1000Mbps RJ45

If you don't know the difference, you probably will not need them. SFP allows you to use different optical or copper links on your hardware by just inserting the right module. So SFP is more flexible (and can be faster) than a built in 1000BASE-T interface but also more expensive. There is also no speed gain compared to a normal 1000BASE-T adapter if you insert a 1000BASE-T SFP module. So if you don't plan to connect the server through optical links in the near future you will not need SFP and you can stay with standard 1000BASE-T.

You might also want to read http://en.wikipedia.org/wiki/Small_form-factor_pluggable_transceiver to understand the concepts of SFP.

The transceiver ports on the switch are typically used for uplinks that connect to other switches that are 100m or more away eg a corporate network may span multiple floors in a building and a switch on each floor would use the SFP ports with optic fiber transceivers and uplink to a core switch. The servers typically would be connected to the core switch using cat6 patch cables not SFP. There is no speed advantage if you connect servers (unless they are 10G ports) however there is a distance advantage. Depending on the transceiver, with SFP you can get 500m plus distance at 1Gbps. Cat6 at 1Gbps is max 100m.