A bit confused about use of Ringer Lactate in blood loss

Hello to you all, I am a nurse student in Italy and interested to become an EMT. 

I am a little bit confused whenever to give N/S 0,9 or Ringer Lactate to a *trauma*/injured patient, meaning a patient that has significant blood loss let's say after a bike accident. 

To get to the point, yesterday I witnessed a bike accident, a man of 50 years old was laying on the ground , his face was covered in blood and as a Doctor said from the crowd, this man had a severe Traumatic Brain Injury after he examined him. 

My question is, 1)Let's say EMTs arrive at the scene,patient has lost a lot of blood so he needs IV fluid to prevent Hypovolemic Shock. What is the best fluid to give to a Traumatic Brain injury patient? Months before I believed that RL was the best choice until a friend of mine (who is a nurse)told me to N E V E R give Ringer Lactate to a Traumatic Brain Injury patient cause the brain edema will get worse. So in this case what fluid should you administer? Normal Saline will do the exact same thing, it will increase brain edema as it is also isotonic as RL, so that looks like a dead end to me. 

2) Now, speaking of a patient that has a significant blood loss NOT from a head injury, let's say he is bleeding from his leg or his hand, he is loosing much blood, as an EMT what is the best choice of fluid restoration? Should you give Normal Saline, Ringer Lactate or what to again, prevent a Hypovolemic shock and restore blood/fluid loss. 

In a few words, to put it simpler, what IV fluid is the best for a blood loss patient with hemorrhage from the head AND from anywhere else in the body.  In what case should I use RL or Normal Saline ? 

Sorry if this is too long for you to read, and forgive any grammar mistakes, English is not my native language, thank you!