I much prefer
Alexander.
Xander is so annoying, hipster and as far as I can tell, traces most of its use to
Buffy the Vampire Slayer, a show I never got but everybody else my age seemed to love it.
I do think
Sandy is a nice, though old-fashioned, nickname for
Alexander. Not used much for men in the US though it is a popular nn for
Sandra;
Sandra is fairly dated here too but is still well-used. It seems to be especially popular with Hispanic girls.