He'd never admit it- Alan
He'd never admit it, not even under the threat of being force-fed the worst of Grandma's kitchen disasters, but Alan just didn't trust Thunderbird One. It was stupid, irrational and illogical, he knew that and recognised it- a relic from when he was much younger- but he just couldn't shake his instinctive distrust of the first response rocket-plane.
As far as his subconscious was concerned, One had killed Dad.
He'd read the reports about that awful day of course, when he'd gone fully operational and gotten access into all of the archives, and while he could read the pain and grief in every line of the report that Scott had written, the sparse lines didn't have the full story. He'd tried to fill in the blanks through eavesdropped conversations, but he hadn't gotten very far. The details of what led up to the events of that day wasn't a topic that Scott or John would ever candidly discuss if there was even a chance of a younger sibling listening. All they would ever talk about was the footage they'd gotten via the GDF, and even then it was rarely.
What he knew for sure was that on that fateful day Thunderbird One didn't get 'there' fast enough, wherever 'there' was. When Scott had come home alone on Thunderbird One, his seven year old brain had decided that the blame rested squarely with the Thunderbird that had failed his family and he'd never really trusted One since.
It didn't help that One was a beast to fly, well, at least he found that it was. One wasn't like Two, dependable and steady, Virgil's 'old friend' that he'd sing to, or Three that rumbled around him with a strong bass note, cradled him in the safety of it's cockpit and eagerly responded to every twitch of his fingers, or Four that twisted and played but was predictable, or Five that hung in space like a great bird, hovering and listening and only rarely swooping from it's path. No, One was a wild horse, fighting the rider on it's back.
The other Thunderbirds needed only guidance but you had to control One and it would punish you for every error.
So no. He didn't fully trust One. While he was pretty sure that One wouldn't hurt Scott, the only one who had truly tamed the rocket-plane, he wasn't so sure about the rest of them.