Using spanning tree in ms. Redundant scenario with older cisco routers

[MX]

Hi!
Redundant setup with two cisco routers (C1111, fibre, R1 and c819, LTE, R2).

C1111 support #spanning-tree mode ?
  mst         Multiple spanning tree mode
  pvst        Per-Vlan spanning tree mode
  rapid-pvst  Per-Vlan rapid spanning tree mode 

but c819 only support pvst.

Two connected ms12x two interface/router  (sw1 connects to R1 and R2 and same with sw2). Root=sw1.  It have been work ok but it seems when upgrade to fw15 it becomes alot of problems. Known issue with ms and pvst but no alternative on backup router(R2) 

  R1      R2

    sw1 sw2

some recommendations? 

[alemabrahao]

It will depend, I prefer to use rapid-pvst, but some guys in the community says that msi is better (I disagree).

[cmr]

Connect each router to one switch only, perhaps connect C1111 to both (in MST mode), and if you want R2 to dual connect then upgrade it to a router that supports MST.