I built a Bounty based on the Revell kit quite a long time ago. I think I can claim to have done a reasonably thorough research job on it, and I reviewed the Airfix kit for a magazine when it first appeared. Neither of them is a great kit; both have serious problems.
The Revell kit came out in 1956 - one of the first two or three sailing ships the company did. The basic hull shape is good, and some of the details are really nice. I especially like the figurehead and the crew figures; the detail on them is simply amazing. Virtually every other piece has serious problems. The deck contains all sorts of inaccuracies, the rails around the bow bear no resemblance to the prototype, the spars are over-simplified....I could go on. On my model I used the hull halves, the transom, the hull of the launch, the quarter galleries, the figurehead, and the crew figures, and dropped the rest in the spares box.
The Airfix kit is considerably bigger and more recent, but that's about all it has to recommend it. (One thing about it that I do like is the way the deck is cast, with integral "deck beams" underneath to set the camber.) It appeared in the late 1970s, I believe, at the time when Airfix was having some very serious financial problems. Apparently the designers didn't really understand the plans they were working with. To begin with, they put the hawseholes too low in the bow, thereby setting off a weird chain reaction: in order for the anchor cables to come inboard above the level of the deck, they mounted the whole deck on a pronounced slope that looks utterly ridiculous. The anchor windlass is absurd; the pawl post is backwards and slopes in the wrong direction. Virtually all of the other deck fittings are inaccurate in one way or another, and the spars, again, are so over-simplified in their details as to be near-caricatures.
One feature that's missing from both kits is the copper sheathing for the hull. (Plenty of other plastic kits - e.g., the first Revell Constitution, which is even older - have done a nice job with copper sheathing.) And neither of them has one of the real ship's most distinctive features: the small water closet on the quarterdeck, which became necessary when the captain got evicted from his cabin to make room for the breadfruit plants.
Unfortunately this very famous ship has not been served well by the model kit industry. There have been at least a dozen commercial kits in plastic and wood, but to my knowledge the only one that really looks like the ship is the recent Caldercraft one. It's hard to find in the U.S., and quite expensive. I haven't actually looked at it, but on the basis of the photos in the ads it looks pretty good.
There is excellent documentation about this ship. A good place to start is the book The Armed Transport Bounty, in the Conway Maritime Press/Naval Institute Press "Anatomy of the Ship" series. It has a series of beautiful drawings by John McKay. My only criticism (and it's a tiny one) is that he labels the aforementioned enclosure on the quarterdeck a "flag locker," which I'm pretty sure it wasn't.
Which kit to buy is, I guess, a matter of personal taste. The Revell one, out of the box, looks a good bit more like the real Bounty. (That sloping deck on the Airfix one I just couldn't live with.) The Airfix one probably could be fixed, and would make a bigger model - hence easier to rig and detail.
Sorry to sound a bit negative, but this is a subject I spent quite a bit of time on. It's a shame the ship hasn't been done justice by the model industry.