In terms of tunnel types:

L2TP - works really well from behind NAT/firewalls.  Does not support 
       IPv6 though (at least our implementation), so might not be the 
       best option if you want to add Ipv6 in the future.  Usually
       the option I recommend if someone is behind an LTE modem or
       something.  No encryption unless used with IPSec

GRE - Small amount of overhead, supports both IPv4 and IPv6 on a single
      tunnel.  Does not work from behind NAT.  Requires a small
      script if running from a  dynamic IP.  No encryption unless
      used with IPSec.

IPIP/SIT - Smallest overhead.  Actually creates 2 tunnels (one for v4
           and one for v6).  Does not work from behind NAT.  Requires
           a small script if running from a  dynamic IP.  No
           encryption unless used with IPSec.

OpenVPN - High amount of overhead on the Mikrotik devices (since they
          only do TCP).  Works from behind NAT/Firewall.  Supports
          IPv4 and IPv6.  Encrypted.

At home, I have a cable line from a TPIA which runs over Shaw and use
the IPIP/SIT tunneling method.  I can get close to full speeds and
have not had any issues with blocked traffic.  I believe Shaw's
traffic management doesn't use DPI, so port 25, etc won't be blocked
inside the tunnel.  If you don't have a strong preference, I'd
recommend this method since I have the most experience on the
client-side and can assist a bit better.