Why is there a B backsite spawnpoint in Ascent? 80% of the time someone else spawns behind you by the time you reach stairs and the other 20% of the time you walk into a crossfire between B main, CT and market while being shot from the back...

My friend started the game today and he was confused on who to pick, just wanted to know what is a good character that can show him the basics. I was thinking Sage or Phoenix but idk