I work in a variety of mediums, depending on the subject, or weather, or even my mood. Many reasons will determine why I've chosen a particular medium. I enjoy using watercolour or acrylics or sometimes oils as well as using charcoal and chalk, pastels, plus pencil and ink drawings.
On occasion, some seascapes seem best if done in acrylic or oils as the particular scene requires the use of a palette knife - to add texture, or effect. Quite often - rocks seem to lend themselves to using 'chunky' paint, so I might use acrylics with a palette knife or oils laid on thickly, to give a structural feel, a permanence to them, or it could be they need to be light and wispy so I'd choose water-colour to give a more ephemeral, transitory touch.
It's unique to every painting as to how I choose to interpret the subject & the end result will vary totally of course if I re-do a painting in another medium. That is quite fun to see how it turns out. :)
This can be extremely infuriating as so many times whilst painting there comes a point where it all seems to go very wrong, I want to scrap the whole thing and start again!! I've learnt (hopefully) that this IS part of the process and if I will just walk away from it for a day or two, somehow it 'rights' itself and I can continue . The end results still astonish me- I still think 'did I really create that ?'