Top 3 Roles?
Hud
Being There
Ninotchka
His performance in Hud is one of the best to ever win the Supporting Actor Oscar. He was also very good in his second winning role in Being There, by far the best thing about a film I didn't care for much.
His nominated performance in I Never Sang for My Father was fine but he was outclassed by Gene Hackman, who had the larger and more impressive role as his son.
Pre-Hud Douglas was a charming star, a good actor but never one who particularly stood out. I like some of his films - notably Counsellor-at-Law, Captains Courageous, Ninotchka and Billy Budd - but he tended to either meld into the background or allow his co-stars to outshine him.
Oh, I must mention his memorable late career role in Polanski's The Tenant, too. If forced to pick a top three performances I'd put that alongside Ninotchka and the peerless Hud.