I’ve heard too many negative comments about the Acorn.
Of the ones you have up there, I’d also say Oak, Feadog, and Clarke. They’ll give you three completely different sounds.
I’m not sure if you mean the Clarke Original or the Sweetone, but I’m assuming you mean Original. It will probably need to have the windway flattened a bit. It will take a LOT of air stock - expect to run out of breath. It has a nice mellow, flute-like tone. It’s also a little odd in the mouth because of the flat angled wooden fipple. It has a very different sound than the Feadog/Generation camp.
The Feadog has much more bite. It’s got a tone similar to a Generation, but a little huskier. It’s a little harder to play stock. It takes a little better breath control, so you may get some squeaks and squawks in the beginning. I’d suggest the blu-tac tweak for this one. The tone is great though, and it gets easier to play with the tweak and some experience.
The Oak is more sweet/pure and quiet. A lot of people say they don’t like it, and many others love it. I think that many of the folks that don’t like it haven’t spent enough time with it. It doesn’t take much breath. If you give it too much air, it doesn’t sound as nice. However, if you get “In the Zone” with it, it’s a very nice whistle. Also with the triple nickel coating, it’s a little heavier and more substantial feeling. In addition, I think it’s got the best intonation of the cheapies I have. When I got my Hoover Whitecap, I bought a second Oak to put it on - very nice whistle. 
Another option is a Clare. I ordered a brass one but The Whistle Shop was out, so Thom sent me nickel. Frankly, it has a small dent in it, and looks a little cheap because it has no sticker or any kind of identifying marks. However, it’s got a really nice tone and is easy to play. I think the intonation is off a bit on mine, but I haven’t checked to see if the tone holes might need some cleaning. I think the price may be a bit high on the nickel Clare, but if the brass one has a similar sound and playability, you might consider it as well.
But if you are only getting three, I’d say Oak, Feadog, and Clarke Original - just for the differences in tone and playability.
Jason