I agree that under pressure situations a semi will be "more reliable" than a pump for most people.

Most inertia semis are not the best in unusual situations where the gun is not going to be held against the shoulder, as they cannot cycle properly.

So, best for HD would be a gas semi, short barrel, slightly shorter buttstock, extended mag tube. The Beretta 1301 is where it's at currently, but they are expensive.

If buying new on a budget, the Mossberg SA20 tactical version is awfully nice but I don't know if there is a mag extension available. Mossberg SA20 tactical