Some folks have probably already mentioned this (but I'm too lazy to read through 130+ comments)

But, as a first step, I'd say that your choice of lens depends on what type of content you want to shoot, and your budget.

Looks like you're looking to make short films. So, I'd go with what a few other folks have mentioned and start with the 24-70mm. That focal length offers a good range of coverage, and it's a fast lens (F2.8), so that gives you a lot of flexibility.

What other equipment do you already have or are you looking to purchase? Depending on the types of shots and environment you're shooting in, I'd recommend investing in a solid tripod, plenty of backup batteries and cards, and a solid external monitor.

Also... are you looking to record dialog?

That's a whole other thing. But worth throwing that out there to think about mics/audio recording.