A couple of aircraft that I did an about face on that come to mind (with appologies for the naivety of youth):
EE Canberra
As a kid, I saw pictures of it in books but there usually wasn't much info to accompany those pictures. To my mind, it was this very boring looking bomber. Seeing pictures of the variants with the offset fighter style canopy that led me to think "Who does that?!" didn't help me see it in any better light.
Fast forward to my late teens. I found a book in the public library dedicated to the Canberra and decided to give it a second look. That book left me floored that I had given so little thought to an aircraft that was essentially the heir to the DeHavilland Mosquito, an aircraft I liked very much.
I had no idea, until that point, that the Canberra was as versatile as it was.
Let's just say the aircraft got a new fan that day.
F/A-18 Hornet
I was about 10 when the Canadian military started taking the Hornet into service. The first time I saw a Hornet at an airshow was 1982, and there were CF-101 Voodoos there as well. On the ground, the Hornet looked underwhelming to me compared to the imposing beast the Voodoo was.
At that same show, the Hornet went up and did a very well recieved demo. That demo was followed not long after by four Voodoos. While not close to the aerobatics of the Hornet, you could feel the Voodoo show as much as see it. To finish off, the Voodoos did a low, four ship dirty pass along the flight line that could shake the fillings out of your teeth.
To me it was like the Voodoos saying to the Hornets parked below" "Ok, kid, you're good, but you'll never be THIS good."
It was exactly the sort of thing that impressed 10 year old me. I was a Voodoo fan and stayed abivalent to the Hornet until my mid-teens.
Until my mid-teens, my knowledge of the Hornet was that it was this multi-role type that was developed from the loser to the YF-16. In a nutshell, I thought the Hornet was the YF-17 that got a lucky break. To my mind, the Canadian military had settled for some sort of warmed over something or other.
I was in the Royal Canadian Air Cadets youth organization by that time and it gave me a few opportunities to not only get up close to the Hornet, but also talk at some length to pilots and ground crew. In doing so, I came to realize that the only thing YF-17 about the aircraft was the physical resemblance. Canada hadn't "settled" for anything, we had a right proper modern combat aircraft in the Hornet.
The more I learned about the Hornet, the more I warmed up to it and respected it.
Knowing that the Canadian Hornets soldiering on these days are still the old A and B models taken on in the 1980s that have been given upgrades at times when they could have (and should have) been traded in for C and D models makes me respect the Hornet that much more for durability.