It depends largely on the particular settings of each network. However, in most cases, MPLS is faster. And that is no wonder because MPLS doesn't encrypt traffic and thus saves time. Theoretically, MPLS  could even boost the connection speed, since each router does not need to perform an IP lookup.
Almost all VPN applications may slightly slow down internet speed since it reliably ciphers your data and routes it through the virtual server, thus taking additional time. However, even despite these additional steps, some Virtual Private Networks still speed up traffic.