Wow, this is an athletic bloodline! Just a few observations I would point out. I think that the photo of Firewater Finale was probably taken when he was about 2 years old, and the photo of Ima Firefighter looks like it was taken when the horse was in his teens. So it would be better to compare these five if you had pics of them at the exact same age.
Based on the photos alone, here's who I like, best to worst:
1. Firewater Finale is my favorite, he's so compact and exactly proportioned in three sections. You can look at his topline from wither to croup and it's about half what the underline is, which is perfect. His head is held higher than any of the other stallions, which gives him a ewe-neck appearance I don't like, but I think if the photo were taken with his head lowered a smidgen he would look perfectly balanced. He looks like a real athlete, and has contributed to the barrel horse world himself.
2. Zanton Firewater has that old-time Quarter Horse look to him. He reminds me of Two Eyed Jack in this photo. Beautiful muscle, great shoulder (all of these stallions have impressive shoulders!), deep heartgirth, short back, pretty much everything a horse should have.
3. A Firewater Twist RB has the Western Pleasure look, and while he may be the most attractive and eye-catching horse of the five, I place him third because he doesn't look as athletic. His back is a little longer, his neck ties in a little lower, he looks a little heavy on the front end and built downhill. Still has a great shoulder and balanced appearance, but not as athletic.
4. Ima Firefighter was probably quite a horse in his younger days, but this photo shows him with a lack of muscle and not the proportions I'd want to see in a stallion of his breeding. His head and neck are overbalancing the rest of his body, and again it makes me think this is a photo of an older horse who is still beautiful but can't compete with the younger stallions in this category as far as body condition.
5. Firewater Fred Jones is placed last, and I'm having a hard time pinpointing what I don't like about him. He's a beautiful horse, but has almost a Morgan-like appearance, and seems much smaller than the other stallions. Again, he has a beautiful shoulder, and great muscle. But look at his topline compared to his underline...something like a very short croup is making his back appear long. Maybe I don't know what I'm talking about here, and if so, someone please correct me. But I just didn't care for his build as much as the other stallions.
Fun question, Daisy! Keep 'em coming.