All trains are safe.

There are 2 direct high speed trains, at 7:32 and 15:40. They can be booked via eurail.com for €10 in 2nd and €13 in 1st class, plus €2 booking fee.

There's also a direct intercity train, leaving Barcelona at 8:30, but it takes 11 hours instead of just under 6.5 hours. Reservation is €6.50 but it can't be booked online.