I consider legst to be one bodypart.
It's really difficult to maximize results if you split up your leg workout. Exercises like presses, squats & lunges work glutes, hams & quads all at the same time. Even calves to some extent. Basically you've warmed up & got the blood flowing to all of those muscles, so it's most effective to continue with the more muscle specific exercises.
That said, working your entire lower body at once is long & exhausting. If it will discourage you, then split it up. You have to do what works for you. If you'd be more likely to stick w/a split routine than enduring the dreaded leg routine (believe me I dread this every week & have a tremendous feeling of accomplishment every time I finish), that's what you should do.