OK I know that Frostfire did some really bad things, like capturing Morningleaf, hunting down Star and threatening to kill him, and torturing Echofrost(kinda), but hear me out on this!
Frostfire would be a really good friend to have. He's protective, he's strong, brave, selfless, determined, open minded, strategical thinker, and a great leader.
He's not a bad pegasus, nor is he a bad character- he's just made bad decisions. But, bad desisions doesn't make a bad character.
Which leads me to say that I personally love Frostfire's character and his arc. How he started to trust Star in Windborn and how they relied on each other. But, that's for a later debate lolol
When you REALLY think about it, Frostfire is just following orders. He is just doing what he was trained to do from yearling age- be a good soldier and follow/give orders. If he was raised in Sun herd or Jungle herd(or any other territory beside Mountain/Snow herd) he would end up a LOT different than how he actually is in the series. For one, he wouldn't have Rockwing and Petalcloud controlling him with an iron fist. He would be free from the tyranny of those two power hungry steeds-and therefore having a better childhood and more freedom in life.
So, yeah, overall, I would want to make friends with Frostfire, even if he has some anger and trust issues, he is a very reliable pegasus.
****thx for listening to my random and worthless rant****