I got this answer from a friend of mine. He's quite experienced so I think his opinions are dependable.
IPCOP is a Home / Small Business Office Firewall Appliance.
Mikrotik's ROS (Router OS) is a full blown enterprise class Router / Firewall / WISP appliance.
IPCOP is way easier to setup, manage, and monitor.
ROS has a much steeper learning curve, but offers a full enterprise class set of features (for a price).
At the most basic of comparisons (i.e. do they secure your network?) - they're the same.
Pick the one that works best for your unique security needs.
FYI: You can get a eval ROS license for free, and the full blown license is cheap (i.e. $100 ish USD).