Seeing that you're in the UK, I'd suggest Ilford's chemicals, LC-29 or Ilfotec HC (HC is a clone of HC-110, while LC29 is just a slightly more dilute version of Ilfotec HC) or even DD-X, which will be a little more expensive at 1+4 and not so much at 1+9. Even cheaper would be Ilford PQ Universal, at 1+29 and above. These are easy to work with liquids. LC-29 might be the best to start with and you might find that starting with the dilution of 1+29 is a good idea.
Although you have to mix it, ID-11 is hard to beat.
I personally love Rodinal, however, I have my developing times and methods worked out for it.
If you do a quick Google search over here, you'll get as many answers as you have time to read. It really doesn't matter which one you choose, especially in the beginning and later you can bend tonality the way you want it, but e.g. the way grain is rendered will remain what typical is of the developer, so even if Ilford says ID-11 1+3 is their sharpest powder developer, it won't look nearly as good as Rodinal does.
Choose one and stick with it (also true for film, paper, paper developer) for quite some time. Good luck!