Metal strings are ideal, in general, for strumming chords with a pick or for modern fingerstyle arrangements, offering a much brighter EQ than nylon strings, with cutting highs and punchy lows.
The tension is quite high, on average around 72 kg, and the diameter of the strings is rather small on the high E and relatively large on the low E.
The nylon strings are perfect for classical music and for any type of composition that requires an extremely balanced equalization throughout the range of high, medium and low notes.
The tension is much less than metal strings, around 36 kg, and the diameter is fairly uniform from high E to low E.
Less painful to press on the keyboard for a beginner and much easier to pluck with fingers or nails.