Photon vs. SmartFox vs. Electro Server
I was asked at the GDC several times how Photon differentiates from competition (SmartFox was most mentioned, Electro Server second) so here is an quick overview table:
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Photon and Competition
Although this is just a very basic overview it already shows the advantages of Photon: (reliable) UDP, C++ server, extensible in C#, support of any data types.