I used to be very adamant that the best gun to teach a new shooter was a target grade .22 pistol. The reasons are obvious... It is the least likely to induce flinching (especially if you single-load primer-only rounds at first), most likely to show bad technique, and it provides very direct feedback to the new shooter about how well they are doing. If their group is bigger than a dime, you know the fault is 100% in their shooting, not the gun's lack of precision. Several models are easy to single load e.g. the Buckmark...leave the magazine in, thumb a round into place, drop the bolt, fire, and repeat.
I have eased up on that position somewhat because I've come to realize that most people don't really want to shoot accurately. They get bored shooting for group size, and can't really apply themselves. I grant that for more action-oriented people you are better off with large dynamic targets of some sort and at that point the advantage of the high precision target pistol is moot. At that point anything that won't cause bad habits is on the table.
As for revolvers, the only new shooters who really benefit from them today are...for lack of a better term I'll say "hipsters"... people who like to adopt styles that were popular before they were born because image is more important to them than function. If having a revolver helps them have fun, that's going to help them learn so I'm all for it.