by constantly confused
For a list of digital models accredited for grade exams, you may like to check out the AMER (Australian Music Examinations Board) website, via google.au . This is quite interesting.
ABRSM now officially endorses Rolands on its website.
I would look for a sound as close to "live" as possible, excellent and variable touch resistance, excellent repetition, 3 pedals that really work, a really good dynamic range, and long-lasting notes, even when only the fingers are being used to hold down the keys.
Cheaper (slightly) than an acoustic
Lighter to transport and site
Can often be moved in an estate car
Are usually MIDI equipped to interface with other keyboards or computers
Never need tuning
Have other sounds available (harpsichord, electric piano etc)
Sound is usually a recording of a concert grand piano, and little speakers can't cope with it
Lifespan of 10-15 years (real pianos can last 100)
Keys and contacts are prone to breakage
Servicing and spares are expensive, and difficult after 10 years to obtain spares
Not as robust as a real piano
More prone to theft
Cheaper models sound unconvincing
Keyboard feel even on Grantouch types is 'dead'
Need electricity to work
Are uglier than real pianos in most cases
Cheaper models merely amplify a sampled sound for a louder effect, a real piano sounds different when played at different volumes