Compared to MPLS, a L2 solution with 100 Gb/s interfaces between core switches and a 10G connection for each buildings looks so much cheaper. But we worry about future trouble using Trill, SPB, or other technologies, not only the "open" ones, but specifically the proprietary ones based on central controller and lots of magic (some colleagues feel the debug nightmare are garanteed).
If you had to make such a choice recently, did you choose an MPLS design even at lower speed ?
A year ago we built NREN backbone using TRILL instead of MPLS. 40 POPs, no central controller, RFC standardized TRILL protocol i.e. L2 routing using IS-IS, no STP. See my recent presentation at http://md.bts.sk/sanet-100g-2.pdf for more details. Much easier to setup, operate & maintain than MPLS and obviously much lower cost. Based on 6-months production experience, my recommendation would be to stay away from MPLS in the campus. With kind regards, M.