Probably a small one. Huts are small spaces and easy to heat. Stoves need to sit on a non flammable surface and be insulated from the wall behind.
Small is good. 2.5kw would be more than enough. The only problem I've found with wee stoves is that they need re-fuelled more often and you have to chop the logs very short, which is actually a bit of a pain. I've used the "Wendy" from Windy Smithy which was cheap and simple and small but quite hungry and has no "refractory" liner, which I think means it doesn't get as hot inside so may burn less efficiently than a lined stove. Ash tends to fall out the front when opened which is a nuisance. Also it has no "CE" accreditation, so maybe wouldn't pass regs? I've also tried the Burley Springdale which burns really well and is easy to control when lit, but can be tricky to get going in my limited experience. I think that Salamander have a good rep and I think they had a new model out recently aimed at small spaces.
We are building two huts which are well insulated and after much research and conscious of how often stoves are too powerful for the space we are going for hobbit stoves from. Salamander stoves. One reason is that they are cast iron and therefore retain heat. Another salamander stove option is there mini range which looks very impressive but is not cheap but u have full cooking facility
We have come across the Chilli Billie from Chilli Penguin stoves - but with a hut of reasonable size we're now concerned it might not heat the space sufficiently and in a sustained way with a 2.5-3kw output. The next ones up are 5Kw and we're pretty sure this would be too much! - So we're looking for any experiences of these to get some reviews from hutter users of the chilli billie particularly...
I think you will find that it generates plenty of heat. How well your hut is insulated will determine how long it retains the heat for. Some huts are going to be 3 season huts. To be 4 season, they will need to be well insulated.