Yet another exhaust manifold.

Hello

My Valiant has a crack in the exhaust manifold for the 3rd time in 6 years. I am going to replace it again soon. Im wondering which manifold I should choose as far as material. Ive seen a variety of metals available with an array of price ranges. Heck, I have even seen plastic. Anyway, what do yall think? Tired of replacing manifolds.

1970 Valiant, 3.7 Slant Six. Completely stock. 60k orig miles