I started on acid, just one hit of medium quality. I had loads of fun on it, and became a psychedelic enthusiast instantly.
my first mushroom trip was already after I'd gone down the route of doing LSD too often and too irresponsibly, and didn't want to fuck with it anymore. I was very young. At this point I'd been psych-free for about three months. I ate a large starter dose of these mushrooms, somewhere between an 3.5 and 7g. My experience was profound and euphoric in many ways, but turned pretty sour when my parents freaked out on me in the middle of it, causing me to have a potent, terrible time. That's my own fault, though; I don't blame mushrooms by any means.
I say either one of these drugs is a good place to start, provided the dose, set, and setting are agreeable. I would not recommend any of these other chems considering they're all somewhat unpredictable, largely potent, and often carry with them an array of physical side effects.