How to read MOSFET datasheet to determine when the MOSFET is fully on
In this specific case the way you can tell that the second one is a better choice is that Rds(on) is specified down to 4V, but in the first one, Rds(on) is specified only at 10V.
In power switching applications I usually try to stick to MOSFET's that have Rds(on) specified at the Vgs I will be using (or lower).
Vgs(th) is only marginally useful in figuring out power switching applications. The reason is that Vgs(th) is usually defined as the gate-source voltage when drain current = 250uA or 1mA or some other low current. In order to switch a high current with low Rds, the voltage will need to be much higher than Vgs(th).
Vgs(th) may be a useful parameter in cases where the drain current you plan to switch is very low, comparable to the drain current used in defining and measuring Vgs(th).
In cases where Rds is not specified at your voltage, you may be able to figure it out or at least constrain the possibilities by studying the curves in the datasheet. But it is easier to find another FET that has guaranteed Rds at or below the voltage you plan to use.