Why is this the favorite when the years older x230 takes up to 16GB ram ?
Many people like the x220 best, because it has the old-style keyboard (does the x230 as well?). The x250 has surprisingly similar performance but much better battery life.
Which is better? I don't know, but I bought a x250 back in 2015 and am still using it as my personal laptop. It only sees light duty these days.
No, but you can fit an X220 keyboard into the X230.