I'm a physio as a bit of background.
The three are very different, but none the less rewarding. What do you want to do?
Osteopathy is the most similar to my education in physio, and I would say that if I'm being honest, whilst I enjoy being a physio, there are times where I wish I could do a bit more in terms of prescribing drugs. I think you will get this with osteo. Thing with physio is we now have prescribing rights in the UK for a limited list of medications, so when I am senior enough and can get on a course, then I can go down that road to a limited extent. I did consider medicine, but decided it just wasn't what I wanted ultimately. I think it's easy to get caught up in the glamour of being a doctor, but the reality is it is flipping hard work. The junior doctors I work with are flat out all day everyday, and often stay late. Ontop of this consider that you will be studying in your spare time for exams every year for your F1, F2 years and then up to 10 years after this depending what speciality you go into. My mate is in his second year of specialist training in Trauma and orthopaedics, and his life is consumed by it. Exams, exams, exams.
Things in the NHS are changing a bit, but from an osteo point of view, it is still dominated by physios in terms of rehab. So, this means that you graduate as an osteo, and you are looking at setting up in private straight away as opposed to having a big employer such as the NHS to go for. This may continue to change as the any willing provider agreement gathers more pace, but I am yet to meet anything other than physios in rehab roles in the NHS. Something to consider I guess if you are thinking about employment - other than some private companies, there is no employment with osteo from my understanding, it's go alone from the off, and I would find this intimidating. Two years into being a physio and I still like the buffer of having seniors to ask when I get stuck. Not going to get that in sole practice, although I would say that an osteo comes out more prepared than a physio for MSK roles.
Nursing, well I don't envy them at all, and I think they are the hardest working people in the NHS. Early, late, nights, weekends. You will get it all. From what I have witnessed on the wards you will get hugged, spat at, shouted at, punched, kissed, groped, and I'm sure that is just a microcosm of what goes on. You will have the most contact with patients, and as such build the best bonds, but this can work both ways. Yes you get your lovely old dears who want to bend your ear all day long, but you will also bear the brunt of anger and sadness. I can see why someone would choose to do nursing, but definitely not for me.
Can you get work experience with them? Possibly the only way of finding out for sure. I think if it were me, out of the three you have listed, and if someone waved a wand and I was qualified, I would go down the medicine route, but there is no way now I could spend another 4 years being lower than pond life training to be doctor, then a further two being only slightly higher than pond life, and then the best part of a decade working up to consultant with endless exams.