The best defender iv ever had is a 'LB with a free kick special' the best midfielder is a 'CM with a free kick special' and the best striker was a 'ST with a one on one special'
So i think that the free kick special ability is definetly a good one. I am sceptical about 'one on one scorers' as my ST with a 'corner taking special' has scored twice as much as my 'one on one scorer' this season. I think its a bit random to be honest.