Which is better SMPI DOHC or Ti-VCT? I'm looking at a Ford Explorer and I don't know which is better

Which is better SMPI DOHC or Ti-VCT? I'm looking at a Ford Explorer and I don't know which is better

They are different things and are not comparable.

SMPI = Sequential Multi Port Fuel Injection. This is how fuel is introduced into the combustion chamber. Most cars have multiport fuel injection. Though Direct Injection is becoming more and more common these days

DOHC = Dual Overheard Camshafts. There are two camshafts positioned in the cylinder head(s). For an inline engine this means there are two camshafts, for a V engine, there are four camshafts (two per head).

Ti-VCT = Ford's brand name for variable valve timing. Ti-VCT adjusts both the exhaust and intake sides.

The 3.5L V6 in the newer explorers has all three; multiport fuel injection, DOHC, and Ti-VCT.