Probably 90% of their food is the same stuff wrapped up in a different shape, they're spooning the same meat into the tacos as the burritos as the crunch wrap etc.
So if your goal is to get a full sense of what taco bell has to offer, get a hard taco, a soft taco, a Doritos taco, and a chalupa, mix and match the meats, sauces, and other toppings, and you'll have a pretty representative sample of most of the menu.
As far as personal recommendations, I like steak chalupas, chicken crunchwraps with chipotle sauce, any variety of their grilled burrito, and their cinnamon twists. Sometimes they have a limited time specialty item that's pretty good, not sure what they're pushing now but always worth checking out what they have.
I will also say that if you don't get a Baja blast you're doing it wrong