Others have said it already, but yeah 2C-B makes a great first psychedelic. I would say of the three you listed, 2C-B is easily the most gentle and least powerful, and after that LSD is probably a good choice, a moderately low dose if you don't have any troubles with 2C-B. LSD is really great, but quite strong. However, except at high doses it leaves you feeling like yourself, just different. Mushrooms, for many people including myself, are much more intense, and they sort of grab you and pull you along for the ride. The best trip I ever had was on mushrooms (and it was my first trip ever on anything too), but I have also had a lot of difficult moments or even entire trips from mushrooms.
A few things to keep in mind with psychedelics... body load can be a thing, especially on the come-up. I always think of psychedelics as giving you the hangover first but leave you feeling great afterwards, the come-ups are uncomfortable oftentimes, especially when you're inexperienced, because the shift from normal consciousness is kind of jarring. 2C-B is very light in this regard, but you may still feel quite uncomfortable at first (or you might not). Part of it is how much you tend to get nauseous because coming up can often cause nausea which adds to a feeling of discomfort. With some strong psychedelics like mushrooms, the come-up can lead to feelings of dread or regret, like "oh no I've poisoned myself, why did I do this? I wish I just felt normal again", etc. If you start to feel this way, remember: you took a drug, and you're coming up, it's normal to feel this way right now, it will pass. If you can just deal with it for a bit, you'll pass through it and hit the peak, and the body issues will melt away and the trip will be great. With some drugs (this is unlikely with 2C-B) you'll experience intense periods that can be unsettling or frightening during the peak of the trip too (for example, "I've gone crazy, I won't ever come down, I broke my brain"), and the same thing applies: remember, you took a drug, you'll come down, you'll be okay. If you avoid panic, it will all work itself out and you'll probably learn something as well.
For the record, LSD has about the nicest come-up and least bodyload of any psychedelic, for me. 2C-B is also very gentle (and the body high during the trip feels really good).