Best Tunnel to use in my network?

I have been running the current configuration for a while now with minimal problems. I have 3 internet connections that all tunnel to a Data Center. The network runs OSPF and does ECMP and fail over etc. I am just wondering if L2TP is the best way? It works, but I am just wondering if I should be doing it another way? L2TP means all packets are fragmented at 1460 MTU. Probably no way around that right? I’d like it to run like there was no tunnel at all. IE, someone does ping with -f and 1500 bytes it will work just like normal. All routers are Mikrotik. Mostly RB1100’s and a few RB450G’s
MY LAYOUT.jpg