brittle stars are fine.. avoid green as they can get aggressive/mean..
Blacks are neat.. be aware they can get pretty darn big fairly quickly..
I started with a small ~2" across one and it was 24" across in under 2 years..
They really only come out at night though and will usually just stay hidden under rocks,etc..
Oh and they WILL dig out sand so ensure your rocks are stable/sitting on glass or whatever..