Updated: May 24, 2021
A keyboard with full size keys is a good starting instrument.
On this you will be able to learn the note names, positions and how to play in rhythm. Some keyboards will be able to produce a good legato and staccato and have the option of a pedal.
You will not be able to learn dynamics or the variations of touch is response to the weight of the piano keys so a piano will feel heavier.
A keyboard will last to TQP Level 2 to 4.
It can be used longer however certain skills will not be developed as easily.
An electric piano is often a keyboard which looks like a piano but does not respond like a piano. It usually is touch sensitive, but it is not as sensitive as a piano.
An electric piano will last to TQP Level 3-.
A studio piano is a digital piano that you can move, take with you to relations or functions. They will require a good keyboard case and you can buy them with wheels. They are weighted and use a pedal on a wire.
A studio piano will last to TQP Level 7.
A digital piano is usually in a cabinet, or has semi-permanent legs. The pedals are lithe same as a normal and the keys are weighted. This option has the advantage, as do all the above, or a headphone socket.
A digital piano will last to TQP Level 10.
It is often said that an acoustic piano is always best, this is not quite correct. Whilst many acoustic pianos are better a good digital piano can respond better than an old out of tune acoustic. If you are going to invest in an acoustic piano there will be a tuning bill twice a year, currently this is £50 in the UK.
A good acoustic piano, with all the keys and pedals working will last you to TQP Level 12 and above depending on the age and quality..
I cannot deny I prefer playing on a grand piano. If you have the space and the finance it is the preferred option. When I bought my first I was going to put a table cloth on it with bar stools and sell the dining table. Music is that important in my home, luckily my first home had the space so it did not happen, however there is still time :) . Any acoustic or grand piano, before you buy, should be checked by a trust worthy technician before you buy it. Whilst acoustic upright pianos are often moved in a 'my mate has a van' fashion, I would not recommend that for a grand piano, please use a professional.